Hippocampus Function and Memory Encoding

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Questions and Answers

What role does the CA3 region of the hippocampus play in memory encoding according to later research?

It functions independently without connections to other regions.

It encodes sequences of events through heteroassociation. (correct)

It only strengthens links between similar memories.

It is solely responsible for autoassociative memory.

Which mechanism initially described the CA3 region's function in encoding memories?

Synaptic degradation process.

Heteroassociation mechanism.

Autoassociative mechanism. (correct)

Asymmetrical association network.

What does the interaction between the DG and CA3 networks demonstrate?

They provide a means to link different components of a memory. (correct)

They only encode information related to animal sounds.

They function independently with no reciprocal connections.

They reinforce autoassociative mechanisms alone.

What is a potential problem associated with the encoding method of the CA3 if it operates alone?

It may propagate degraded representations of memories. (C) Signup and view all the answers

What may occur when only some components of a memory are retrieved according to the autoassociative mechanism?

Memory retrieval will be incomplete and fragmented. (C) Signup and view all the answers

What is the primary function of mossy fibers in the hippocampus?

They transmit signals from the Dentate Gyrus to CA3. (A) Signup and view all the answers

Which layer in the Dentate Gyrus is primarily composed of principal granule cells?

The principal cell layer. (B) Signup and view all the answers

In the hippocampal structure, which layer is noted for having pyramidal cells arranged orderly?

Pyramidal cell layer. (D) Signup and view all the answers

Which of the following statements about dendritic structures in the hippocampus is incorrect?

Monopolar cells have dendrites that extend in multiple directions. (B) Signup and view all the answers

Anxiety in rodent behavior is primarily associated with which specific function in the hippocampus?

Control of impulsivity. (A) Signup and view all the answers

How are the principal cell layers in the hippocampus differentiated?

According to their size and appearance. (B) Signup and view all the answers

Which statement accurately describes the structure of the layers in the Dentate Gyrus?

The molecular layer is acellular and sits above the granule layer. (C) Signup and view all the answers

What does hyperexcitability in the hippocampus primarily refer to?

Reduced threshold for neuronal firing (B) Signup and view all the answers

Which type of seizure remains focal and doesn't spread to other areas of the brain?

Complex partial seizure (C) Signup and view all the answers

What is the main intracellular correlate of interictal EEG spikes?

Paroxysmal depolarization shift (PDS) (B) Signup and view all the answers

In the context of Alzheimer's disease, what is a significant symptom related to the hippocampus?

Inability to form new memories (C) Signup and view all the answers

What finding is characteristic of schizophrenia regarding the hippocampus?

Failure to recruit the hippocampus during memory retrieval (C) Signup and view all the answers

Which of the following is NOT a hallmark of seizures?

Histamine release (B) Signup and view all the answers

How is a tonic-clonic seizure characterized?

Sudden loss of consciousness followed by rhythmic contractions (D) Signup and view all the answers

Where is Alzheimer's pathology believed to first become apparent in the brain?

Entorhinal cortex (A) Signup and view all the answers

What could happen if post-PDS hyperpolarization fails in the context of epilepsy?

Ictal discharge may occur, leading to seizures (D) Signup and view all the answers

Which type of neurons primarily become hyperexcitable during seizure activity?

Glutamatergic neurons (D) Signup and view all the answers

What is the primary function of feed-forward inhibition in pyramidal neurons?

To dampen the effects of afferent excitation (A) Signup and view all the answers

Which layer do apical dendrites travel through in the hippocampus?

Stratum radiatum (A) Signup and view all the answers

What role does the CA1 neuron serve as in the hippocampus?

A temporal coincidence indicator (D) Signup and view all the answers

Which neurotransmitter receptors are mainly affected by the prolonged IPSP in pyramidal neurons?

GABAA and GABAB receptors (D) Signup and view all the answers

What do local field potentials represent in the hippocampus?

Summed electrical activity from a large number of cells (A) Signup and view all the answers

Which type of dendrites extend longer in pyramidal neurons?

Apical dendrites (B) Signup and view all the answers

The narrowing of the time window for triggering action potentials is due to which feature?

Feed-forward inhibition (A) Signup and view all the answers

What layer do basal dendrites predominantly extend into?

Stratum oriens (A) Signup and view all the answers

What type of pathways connect different brain regions through timing information?

Transverse and septotemporal pathways (A) Signup and view all the answers

What role do CA3 neurons play in mutual excitation within the hippocampal circuitry?

They create a positive-feedback cycle leading to hyperexcitability. (A) Signup and view all the answers

Which type of interneurons target distal dendritic sites in the CA3 region?

Oriens-lacunosum moleculare (O-LM) cells (C) Signup and view all the answers

What are the implications of recurrent collateral circuitry in CA3 neurons?

It increases the vulnerability to overexcitation. (D) Signup and view all the answers

What is the primary function of the Schaffer collateral pathway?

It projects axons of CA3 pyramidal neurons to CA1 neurons. (C) Signup and view all the answers

Which condition is the hippocampus particularly vulnerable to due to its excitability?

Schizophrenia (C) Signup and view all the answers

How do some interneurons in CA3 synchronize their activity?

By forming dendritic gap junctions. (B) Signup and view all the answers

What may result from over-stimulation of NMDA receptors in the hippocampus?

Pathological increases in intracellular calcium. (A) Signup and view all the answers

What is a primary characteristic of CA3 to CA1 synapses?

They exhibit high levels of plasticity. (B) Signup and view all the answers

Which type of interneurons in CA3 targets both perisomatic and distal dendritic sites?

Trilaminar Cells (C) Signup and view all the answers

What type of connections do CA3 neurons have with neurons in the contralateral hemisphere?

Reciprocal projections (C) Signup and view all the answers

What effect does administering AP5 have on water maze performance during training?

Increases latency to find the platform (A) Signup and view all the answers

How do HPC-lesioned rats perform in spatial reference memory tasks compared to control rats?

They exhibit increased latency in locating the platform (D) Signup and view all the answers

What is the primary synaptic change associated with inhibitory avoidance training?

Enhancement of fEPSPs in CA1 (C) Signup and view all the answers

What deficits are observed in CaMKII mutant mice during water maze tasks?

Impaired swimming to both visible and hidden platforms (D) Signup and view all the answers

What is the consequence of preventing LTP during a learning experience?

Disruption of memory encoding for that experience (B) Signup and view all the answers

Which property of long-term potentiation (LTP) indicates that weak stimulation alone does not induce LTP?

Cooperativity (A) Signup and view all the answers

How does simultaneous tetanus to two inputs influence the induction of LTP?

It enhances the weak input's response due to association with a strong input. (B) Signup and view all the answers

What type of stimulation is required to induce long-term depression (LTD)?

Repetitive low frequency stimulation (B) Signup and view all the answers

Which receptor type plays a crucial role in the induction of LTP, particularly in response to strong stimulation?

NMDA receptors (C) Signup and view all the answers

What effect does long-term depression (LTD) have in relation to LTP?

It can undo the effects of previously induced LTP. (D) Signup and view all the answers

What is the typical duration of LTP, as demonstrated in the longest in vivo experiments?

Up to 1 year (A) Signup and view all the answers

What is a defining characteristic of Long-Term Potentiation (LTP)?

It requires stimulation and has long-lasting effects. (C) Signup and view all the answers

Which characteristic does NOT pertain to NMDA receptors in facilitating LTP?

They are anti-correlated with long-term depression. (B) Signup and view all the answers

Which property of LTP refers to the requirement of stimulus intensity for its induction?

Cooperativity (B) Signup and view all the answers

What happens during post-tetanic potentiation (PTP)?

It results in increased PSP amplitude after a delay following tetanus stimulation. (B) Signup and view all the answers

What is the primary action of LTP with respect to synaptic efficiency?

To enhance synaptic connectivity and transmission strength. (B) Signup and view all the answers

Which mechanism best explains why strong stimulation induces LTP but weak stimulation does not?

Threshold for synaptic activation must be exceeded. (C) Signup and view all the answers

Which mechanism is NOT associated with Long-Term Depression (LTD)?

It occurs in response to high-frequency stimulation. (D) Signup and view all the answers

Which of the following does NOT characterize the experience-dependent nature of LTP?

It can be triggered by random, uncoordinated activities. (D) Signup and view all the answers

What is the expected duration of change in synaptic strength for short-term synaptic plasticity?

A few minutes or less (D) Signup and view all the answers

What role does coincident activity play in the process of LTP?

It requires simultaneous activation of presynaptic and postsynaptic cells. (B) Signup and view all the answers

What is primarily responsible for the increase in synaptic transmission during LTP?

Increased sensitivity of postsynaptic cells to glutamate (D) Signup and view all the answers

What major factor contributes to the postsynaptic expression during early-LTP?

Activation of silent synapses (B) Signup and view all the answers

What changes are characteristic of late-LTP?

Changes in gene expression and protein synthesis (D) Signup and view all the answers

What structural change can be observed following the induction of LTP?

Increase in synaptic contacts and size (B) Signup and view all the answers

Which type of calcium concentration leads to long-term depression (LTD)?

Slow and minimal rises of Ca2+ (A) Signup and view all the answers

What type of effects can LTP and LTD have on synaptic efficacy?

Both homosynaptic and heterosynaptic effects (C) Signup and view all the answers

What is a shared requirement for both LTP and LTD regarding calcium signaling?

Both require a rise in postsynaptic calcium concentration (D) Signup and view all the answers

What is often observed as a result of facilitated synaptic transmission during brief stimulation?

Gradually decaying facilitation (B) Signup and view all the answers

What role does calcium play in the mechanisms of LTP and LTD?

Calcium is crucial for both LTP and LTD induction but results differ (B) Signup and view all the answers

What factor has not been conclusively tied to learning and memory despite correlations with LTP and LTD?

Definitive relationship between synaptic changes and memory formation (C) Signup and view all the answers

What criterion indicates that memorable events should lead to detectable changes in synaptic efficacy?

Detectability (B) Signup and view all the answers

Which of the following best describes 'anterograde alteration' in the context of memory experiences?

Impairing memory formation by blocking LTP during learning (C) Signup and view all the answers

What is indicated by retrograde alteration in memory processes?

Modifying memories of past experiences via synaptic weight changes (D) Signup and view all the answers

Which method was used to assess rats' memory of experiences in the inhibitory avoidance paradigm?

Time taken to cross into a dark chamber (D) Signup and view all the answers

Which of the following cell markers is associated with the induction of LTP after inhibitory avoidance training?

Increased phosphorylation of Ser831 (C) Signup and view all the answers

Which of the following is a consequence of mimicking synaptic weight changes artificially?

Induction of a false memory for non-existent experiences (B) Signup and view all the answers

What cellular changes indicate that LTP occurred after Inhibitory Avoidance training?

Increase in GluR1 and GluR2 protein levels (A) Signup and view all the answers

In the context of LTP, what is the significance of phosphorylating receptor proteins?

It enhances receptor sensitivity and synaptic efficacy (D) Signup and view all the answers

How does the two-chambered box relate to the study of learning-induced LTP?

It allows observation of rats' avoidance behaviors linked to memory (C) Signup and view all the answers

In the study of learning-induced LTP, which control group would provide insights into the effects of shock on learning?

Shock-only group (A) Signup and view all the answers

What can be inferred about cortical processing based on columnar organization?

It primarily represents a small range of stimuli. (C) Signup and view all the answers

Which of the following statements about functional columns is correct?

They may be absent in certain closely related mammals. (D) Signup and view all the answers

What does the evidence suggest about persistent activity in PFC neurons?

It can be explained by discrete functional domains/columns. (A) Signup and view all the answers

Which factor contributes to the understanding of columnar structure in the cortex?

The role of evolutionary adaptations in mammals. (D) Signup and view all the answers

How does the structure of functional columns affect stimulus representation?

It allows for overlapping representations of related features. (A) Signup and view all the answers

What is a primary function of the ventromedial prefrontal cortex?

Motivated decision making and emotional responses (D) Signup and view all the answers

Which layer is characteristic of the neocortex, which contributes to detailed perception and intelligence?

6 layers (A) Signup and view all the answers

Which statement about Brodmann's areas is accurate?

They are based on cytoarchitectural organization (B) Signup and view all the answers

What aspect of the prefrontal cortex does not reach full maturation until around the age of 19?

Myelination of connections (C) Signup and view all the answers

In terms of mammalian cerebral cortex evolution, higher mammals exhibit which of the following characteristics?

More pronounced folding and a larger frontal lobe (A) Signup and view all the answers

What broad function is identified with the association cortices of the cerebral cortex?

Cognition and complex behavior (C) Signup and view all the answers

Which category of cerebral cortex is classified as the 'new' cortex with six layers?

Neocortex (C) Signup and view all the answers

Which layer of the neocortex is primarily composed of dendrites and contains few cell bodies?

Layer 1 (A) Signup and view all the answers

What is the primary function of pyramidal cells in the neocortex?

Major output cells (D) Signup and view all the answers

In terms of connectivity, how are Layers 2 and 3 of the neocortex characterized?

Difficult to distinguish experimentally (A) Signup and view all the answers

How many layers are present in the laminar organization of the neocortex?

Six (B) Signup and view all the answers

What type of cells are primarily found in Layer 4 of the neocortex?

Granule cells (D) Signup and view all the answers

What characteristic defines the structure of the gray matter layer at the surface of the cerebral hemisphere?

Composed of unmyelinated axons (B) Signup and view all the answers

What role do granule cells play in the neocortex?

Recipient of thalamic input (D) Signup and view all the answers

How does the thickness of cortical layers vary according to different cortical regions?

Varies significantly among regions (A) Signup and view all the answers

Which type of neuron dominates the composition of principal cells in the neocortex?

Pyramidal cells (D) Signup and view all the answers

What is a significant change in the prefrontal cortex that occurs in the 7th or 8th decade of life?

Shrinkage and disappearance of dendrites (C) Signup and view all the answers

How did Phineas Gage's personality change after his accident?

He became gross, profane, and irreverent (A) Signup and view all the answers

What type of damage was identified in Phineas Gage's brain concerning the outcome of his injury?

bilateral damage to the ventromedial region of the frontal lobes (B) Signup and view all the answers

Which theory posits that different regions of the prefrontal cortex are responsible for different types of working memory?

Domain Specificity Theory (A) Signup and view all the answers

During spatial working memory tasks, what does a dlPFC neuron exhibit during the delay period when the cue aligns with its preferred direction?

Persistent firing (D) Signup and view all the answers

What type of functions are primarily influenced by the ventromedial region of the frontal lobes?

Decision making, morality, and social skills (D) Signup and view all the answers

What biophysical factor is being explored to understand persistent activity in neurons?

Circuit connectivity within the cortex (C) Signup and view all the answers

Which of the following roles was demonstrated by Phineas Gage’s case regarding the brain?

Certain functions are localized in specific areas of the cerebral cortex (B) Signup and view all the answers

What was a key outcome from the analysis of Phineas Gage's skull using modern imaging techniques?

Reconstruction of the trajectory of the steel rod (D) Signup and view all the answers

Which layer of the neocortex primarily sends outputs to the thalamus and subcortical structures?

Layer 5/6 (C) Signup and view all the answers

What is the main route for sensory information to communicate with the cortex?

Thalamocortical projection to Layer 4 (D) Signup and view all the answers

Interneurons in the neocortex primarily provide which type of inhibition?

Feedforward and feedback inhibition (B) Signup and view all the answers

In the primary visual cortex, which structures analyze specific regions of the visual field?

Hypercolumns (D) Signup and view all the answers

What is true about the cortical microcircuitry organization?

Most axons remain within the cortex. (C) Signup and view all the answers

Which type of input primarily travels through the cortical columns?

Sensory inputs (D) Signup and view all the answers

The concept of 'Barrel cortex' in rats is associated with what?

Sensory input from individual whiskers (C) Signup and view all the answers

Which neocortical cell type is classified as a local neuron that releases GABA?

Interneurons (C) Signup and view all the answers

What distinguishes a complex cell in the primary visual cortex?

It is formed by simple cells summing their receptive fields. (A) Signup and view all the answers

Which feature of neocortical circuitry aids in vertical columnar connection?

Layer-specific input segregation (C) Signup and view all the answers

What is the primary function of parvalbumin interneurons in the amygdala?

FeedBACK inhibition (B) Signup and view all the answers

Which receptor type mediates the fast component of inhibition in principal amygdala neurons?

GABAA receptors (C) Signup and view all the answers

What is a characteristic feature of intercalated cells in the amygdala?

They generate feedforward inhibition. (D) Signup and view all the answers

In terms of connectivity, how must LA inputs influence CeA outputs?

By routing through intra-amygdala connections (A) Signup and view all the answers

What distinguishes CeM neurons from CeL neurons in the central amygdala?

CeM neurons have larger somas and sparser dendritic branching. (C) Signup and view all the answers

Which pathway option is indirect for LA inputs influencing CeM?

LA -> CeL -> CeM (D) Signup and view all the answers

What is the predominant neurotransmitter in the majority of intercalated cells?

GABA (B) Signup and view all the answers

The original model of amygdala function suggested that information flows from which nucleus to CeA?

LA (C) Signup and view all the answers

What is one physiological response phenotype exhibited by both CeM and CeL neurons?

Diverse action potential patterns (B) Signup and view all the answers

What is the primary function of the lateral amygdala (LA)?

Main input gateway for sensory information (B) Signup and view all the answers

Which statement about the basolateral amygdala (BLA) neurons is accurate?

Most neurons exhibit low spontaneous activity (C) Signup and view all the answers

Which type of neurons predominantly make up the remaining 20% of the BLA?

Fast-spiking GABAergic interneurons (B) Signup and view all the answers

What aspect of emotional responses is significantly influenced by the amygdala?

Triggers adaptive responses to stimuli (C) Signup and view all the answers

What is indicated by high levels of µ-opioid and DA1 receptors in certain neurons?

They demonstrate regular spiking firing patterns. (B) Signup and view all the answers

Which characteristic describes the spike frequency adaptation observed in BLA projection neurons?

Progressive decline in firing rate with prolonged stimulation (C) Signup and view all the answers

Which function is primarily associated with the central amygdala (CeA)?

Controlling emotional expression and physiological responses (B) Signup and view all the answers

What is the primary effect of lesions in the amygdala regarding fear conditioning?

Attenuates or abolishes fear unconditioned responses. (D) Signup and view all the answers

What type of conductances contributes to the spike frequency adaptation in BLA neurons?

Voltage- and calcium-dependent K+ conductances (D) Signup and view all the answers

What role does the hippocampus play in the context of extinction training?

It modulates contextual aspects of fear extinction. (B) Signup and view all the answers

How does the infralimbic region of the mPFC influence fear memories?

It exerts feed-forward inhibition to decrease fear memories. (A) Signup and view all the answers

In emotional processing, what has historically been the focus of amygdala research?

Understanding the mechanisms of fear and threats (C) Signup and view all the answers

What behavioral response is associated with the activation of LA principal cells in the absence of a peripheral shock?

Induction of fear conditioning. (D) Signup and view all the answers

What is the implication of having various types of GABAergic interneurons in the BLA?

A potential increase in inhibition mechanisms (A) Signup and view all the answers

What role does the amygdala primarily play in behavior?

Expressing and experiencing emotions (B) Signup and view all the answers

Which psychiatric conditions have been linked to structural or functional changes in the amygdala?

A wide variety, including anxiety and mood disorders. (D) Signup and view all the answers

Which nuclei compose the basolateral complex of the amygdala?

Lateral, basal, and accessory basal nuclei (B) Signup and view all the answers

What is a consequence of reversible inactivation of the amygdala after learning?

It blocks the expression of conditioned responses. (A) Signup and view all the answers

What does long-term potentiation (LTP) represent in terms of associative learning?

A cellular analog of associative learning. (C) Signup and view all the answers

What behavioral condition is associated with a bilateral amygdala lesion, as evidenced by patient S.M.?

Loss of the ability to recognize emotions in faces (B) Signup and view all the answers

How does stimulation of the amygdala affect behavioral states?

It induces a state of heightened increased vigilance (A) Signup and view all the answers

What happens to neurons in the amygdala when novel stimuli are presented repeatedly and are deemed irrelevant?

They habituate rapidly. (C) Signup and view all the answers

The BLA to CeM functional connectivity in individuals with generalized anxiety disorder is characterized by what?

Abnormal functional connectivity. (B) Signup and view all the answers

What evidence provided insight into the amygdala's involvement in behavior?

Lesion studies involving temporal lobe ablations (D) Signup and view all the answers

Which aspect of the amygdala is highly conserved across species?

The primary nuclei and basic circuit connections (C) Signup and view all the answers

Which syndrome is linked to temporal lobe damage, including parts of the amygdala?

Kluver-Bucy Syndrome (B) Signup and view all the answers

What histological criteria are used to distinguish nuclei in the amygdala?

Density, shape, size of cells, and chemical signatures (B) Signup and view all the answers

What is a primary behavioral change observed with selective amygdala lesions?

Impaired behavioral responses to fear-conditioned stimuli (C) Signup and view all the answers

Which structure is part of the limbic system that is known to influence emotions?

Amygdala (A) Signup and view all the answers

What is the primary role of the suprachiasmatic nucleus (SCN) in regulating sleep-wake cycles?

It serves as the master internal biological clock. (A) Signup and view all the answers

Which mechanism is responsible for the generation of circadian rhythms within central clock neurons?

Autoregulation via negative feedback loops. (B) Signup and view all the answers

What physiological processes are affected by circadian rhythms throughout the 24-hour cycle?

Various biochemical and physiological processes. (C) Signup and view all the answers

What effect does exposure to light have on the molecular clockwork of the SCN?

It can lead to adjustments in the circadian cycle. (D) Signup and view all the answers

How are biological clocks, like the SCN, critical for behavioral decisions in daily life?

They influence the availability and efficient allocation of resources. (C) Signup and view all the answers

What are the necessary components for a biological clock like the SCN?

Light sensors, signaling pathways, and output mechanisms. (B) Signup and view all the answers

What is an outcome of the autoregulation process via clock genes?

Completion of a circadian rhythm cycle. (B) Signup and view all the answers

Which neurotransmitter is released as part of the SCN's response to light exposure?

Glutamate. (B) Signup and view all the answers

In what way do circadian rhythms manifest in physiological behaviors?

Through fluctuations in energy levels corresponding to sleep cycles. (A) Signup and view all the answers

What aspect primarily distinguishes sleep-wake cycle regulation from other biological processes?

It is more susceptible to external disruptions. (D) Signup and view all the answers

Which criterion is essential for defining a substance as a Sleep Regulatory Substance (SRS)?

It should enhance sleep while reducing wakefulness. (D) Signup and view all the answers

What role does adenosine play in sleep homeostasis?

Accumulates during wake hours (B) Signup and view all the answers

Which method is primarily used to measure sleep-wake states?

Electroencephalography (EEG) (B) Signup and view all the answers

What is indicated by the amplitude of EEG signals?

Synchronized activity of cortical cells (B) Signup and view all the answers

What is represented by a hypnogram?

The identified stages of sleep over time (D) Signup and view all the answers

What is the importance of thalamic relay neurons in sleep mechanics?

They govern the transition between sleep and wake states. (D) Signup and view all the answers

What do brain transection experiments suggest about the medulla and pons?

They play a significant role in sleep regulation. (A) Signup and view all the answers

Which of the following is a potential candidate for the role of the 'sand' in sleep homeostasis?

Adenosine (C) Signup and view all the answers

What characteristic of sleep staging can be determined through amplitude and synchrony measurements in EEG?

Depth of non-REM sleep (D) Signup and view all the answers

Which of the following questions reflects current inquiries into sleep regulation?

What brain regions are active during wake and sleep states? (C) Signup and view all the answers

What is one of the primary challenges in comprehending the neural regulation of wakefulness?

Different cell types might not share similar functions (A) Signup and view all the answers

Which neural feature is typically high during wakefulness according to firing patterns observed?

Monoaminergic neuron firing (C) Signup and view all the answers

What potential complication may arise from attempting to study neural pathways promoting wakefulness?

Overlapping functions among distinct pathways (C) Signup and view all the answers

How does the activity of basal forebrain cholinergic neurons relate to different sleep states?

They are associated with fast cortical EEG during wake and REM states (C) Signup and view all the answers

What aspect of the firing rates in monoaminergic neurons may detract from understanding wakefulness regulation?

The variability in firing rates across different states (D) Signup and view all the answers

Which factor complicates the investigation into neuropeptide roles during the regulation of wakefulness?

The limitations of optogenetics in understanding co-release mechanisms (B) Signup and view all the answers

What could significantly influence the behavioral outcomes associated with neuronal activity during wakefulness?

Compensation mechanisms from adjacent neural circuitry (B) Signup and view all the answers

Which of the following best describes the activity of thalamic relay neurons during wakefulness?

They exhibit tonic firing during awake states (D) Signup and view all the answers

Which aspect of neuronal circuits is essential to understand when investigating wakefulness states?

Hierarchy and interdependence among diverse neural circuits (B) Signup and view all the answers

What effect does the activation of orexin neurons have on REM sleep?

It suppresses REM sleep. (C) Signup and view all the answers

Which type of neurons promotes NREM sleep by inhibiting wake-promoting neurons?

GABAergic neurons (B) Signup and view all the answers

What primary role do glutamatergic neurons in the sublaterodorsal nucleus play?

Generate REM sleep. (D) Signup and view all the answers

What is the impact of loss of orexin neurons in the context of narcolepsy?

It destabilizes the switching mechanism. (D) Signup and view all the answers

How do cholinergic neurons influence the EEG patterns during REM sleep?

They help drive fast EEG activity. (D) Signup and view all the answers

What is a key characteristic of the sleep-wake 'flip-flop' switch?

It relies on two populations of mutually inhibitory neurons. (A) Signup and view all the answers

What effect does focal restoration of TMN and LC have after orexin loss?

It improves ability to maintain wakefulness. (D) Signup and view all the answers

Which neurons are believed to promote REM sleep induction and duration?

MCH-releasing neurons (A) Signup and view all the answers

What neurotransmitter system is primarily responsible for the induction of NREM sleep?

GABAergic system (D) Signup and view all the answers

What role do GABAergic neurons in the parafacial zone have with respect to sleep?

They inhibit the parabrachial nucleus. (A) Signup and view all the answers

Study Notes

Hippocampus: Overview

The hippocampus is one of the most intensively studied structures in the brain.
Along with the amygdala, it forms the central component of the limbic system.

Coronal Plane of the Hippocampus

Diagrams illustrate coronal sections of the rat and human brain showing the hippocampus's location.

Hippocampus and Cortico-Striatal Loops

The hippocampus is a major component of the "affective" cortico-striatal loop.
It provides limbic information to both the ventral striatum and medial prefrontal cortex.

Patient H.M. - Amnesia

H.M. was a famous case study of amnesia.
He experienced seizures and underwent surgery at 27 to relieve them.
This surgery resulted in retrograde and anterograde amnesia.
While H.M. showed significant memory loss concerning declarative memories (episodic and semantic), short-term memory, procedural memory, language, visuospatial perception and attention remained intact.

Hippocampus Functions

Spatial Learning and Memory/Navigation: Taxi drivers showed increased volume of right posterior hippocampus correlating with their experience. Rodent studies showed 'place cells' within the hippocampus fire preferentially in certain locations.
Context Learning and Retrieval: Rats without a hippocampus do not show freezing behaviour to a context previously paired with shock. Human studies using PET scans show activation in the right hippocampus and ventral pallidum in the context of anxiety.
Working Memory: fMRI studies showed hippocampus activation during maintenance phase of working memory tasks. Hippocampal lesions in rats impair spatial working memory tasks using radial mazes.

Other Theories

Higher-order perception of spatial information (rodents and humans)
Novelty detection (rodents and humans)
Processing timing
Anxiety (rodents)
Behavioural inhibition/control of impulsivity (rodents)

Medial Temporal Lobe Circuitry

Diagrams show the key pathways and structures within the medial temporal lobe.
These include the entorhinal cortex, hippocampus proper, and subiculum, and various connections with other brain areas.

Hippocampus Proper

Well-defined laminar structure that uses clear rows of pyramidal cells.
Transverse brain slices show maintainable circuitry with easily identifiable lamina.
Pathways within the hippocampus include EC->DG->CA3->CA1->Sub.

Hippocampal Network: Transverse Pathways

Information generally flows unidirectionally.
Entorhinal cortex projects to dentate gyrus and CA3 via perforant path.
Dentate gyrus projects to CA3 via mossy fibers.
CA3 projects to CA1 via Schaffer collaterals.
CA1 connects to the Subiculum and projects back to the Entorhinal cortex..

Types of Principal Neurons

Granule cells (unipolar)
Pyramidal neurons (multipolar)

Dendritic Length & Orientation of Principal Neurons

Diagrams illustrate the dendritic morphology of granule and pyramidal cells within the hippocampus.

Summary Notes; Layer/Cell Types

Dentate Gyrus (DG) has three distinct layers: granule cell layer, molecular layer, and polymorphic layer.
The hippocampus has a principal cell layer (CA1, CA2, & CA3) with various strata.

Transverse and Septotemporal Pathways

Details on the transverse and septotemporal pathways which play key roles in cross-plane information transfer within the hippocampus.

Synaptic Inputs to Pyramidal Neurons

Excitatory inputs from extrinsic sources (e.g., entorhinal cortex, thalamus) target pyramidal cells.
Excitatory input from local sources (e.g., CA3) are the main input.
Inhibitory (GABAergic) inputs from local interneurons also affect pyramidal cells.

Intracellular Response to Stimulation

EPSP is followed by a prolonged IPSP (mediated by interneurons).
This feed-forward inhibition serves to control neuronal excitation, enabling high-fidelity transfer of timing information between brain regions.

Intrinsic Electrophysiological Properties of Hippocampal Neurons

CA1 neurons have a prolonged firing pattern characterized by spike-frequency adaptation and a slow after-hyperpolarization (AHP).
CA3 neurons have brief, high-frequency bursts of action potentials involved in theta rhythm generation.

Extracellular Responses in the Hippocampus

Local field potentials represent summed electrical activity from many cells.
pEPSP (population EPSP) recorded from the hippocampus is due to neurons in the same orientation and synaptic inputs in the same area.
Time course of field potentials often matches the underlying synaptic currents.

Hippocampus & Disease, Functional Synthesis of Episodic Memory

The hippocampus is prone to various diseases (e.g., epilepsy, Alzheimer's disease, schizophrenia).
Overexcitation in the hippocampus, involving synchronized firing can result in seizures.
CA3 neurons are notably vulnerable to overstimulation due to recurrent circuitry, leading to pathologies such as increased intracellular calcium and neuronal death.

Epilepsy & The Hippocampus

The hippocampus is a highly epilepsy-prone brain region.
Glutamatergic neurons become hyperexcitable in epilepsy.
Seizure activity can be either focal (complex partial) or spread (tonic-clonic).

Epileptiform Activity in Pyramidal Cells

Intracellular correlates (paroxysmal depolarization shifts (PDS)) of interictal EEG spikes in pyramidal cells are related to epileptic activity.
Failure of post-PDS hyperpolarization can lead to ictal (seizure) discharge.

Potential Mechanism for Epilepsy

GABA interneurons usually control hyperexcitability, but their potential degeneration in some cases can have the opposite effect, leading to epilepsy.
Degeneration of DG interneurons could lead to axonal sprouting and recurrent excitation onto granule cells.

Hippocampus and Alzheimer's Disease

A key feature of Alzheimer's disease is an inability to form new memories and loss/weakening of old memories.
Early brain region involvement in the disease appears to be the entorhinal cortex.
Reduced hippocampal volume often occurs in patients with Alzheimer's disease.

Hippocampus and Schizophrenia

Reduced hippocampal and amygdala volumes are linked to schizophrenia.
Schizophrenia is associated with abnormal baseline levels of hippocampal activity during memory retrieval tasks and a failure to recruit the hippocampus.

Functional Synthesis; Encoding Episodic Memory

Example: encoding of episodic memory: little Jenny dropping cotton candy and a monkey grabbing it at the zoo. Analysis of how this event is encoded, what brain structures are involved, and how the different parts function to create this memory.

Contextual Memory; "At the Zoo"

Lists the contextual elements involved, such as animal sounds and smells, the outdoors/forest smell, animals in cages, balloons, and the smell of cotton candy.
These contextual elements may activate related cells/memories in the hippocampus.

CA3 Microcircuits

CA3 has five types of GABAergic interneurons: Basket, Axo-Axonic, Bistratified, Oriens-lacunosum, and Trilaminar.
These interneurons can target various areas (perisomatic (body), distal) and often work synchronously to inhibit or excite pyramidal cells.

Recurrent Networks Working Together

Encoding of memories can be due to the interactions between two recurrent networks (in CA3 and DG). Decoding of these memories would depend on DG and CA1 working in conjunction.

CA3 Pyramidal Cells – Mutual Excitation

CA3 neurons within the same septotemporal level have reciprocal glutamatergic connections.
Mutual excitation creates a positive-feedback cycle.
CA3 collaterals project back to the DG, making monosynaptic contact with mossy cells.

Schaffer Collateral Pathway (CA3 -> CA1)

CA3 pyramidal neurons project to CA1 neurons via the Schaffer collateral pathway .

Septotemporal Pathways

The pathways that connect the septotemporal axis are labeled by their prominent efferents which correlate with particular cognitive functions like exploration, navigation, spatial learning, emotion regulation and other general cognitive abilities.

Entorhinal Cortex and "Context"

Entorhinal cortex input can directly target CA3 and CA1.
It is also capable of influencing context by creating a depolarizing bias in target cells. Information originating here is likely passed to CA3 which would influence firing patterns.

Function of CA1 and Hippocampal Output

CA1 region acts as a decoder and conveys information to the entorhinal cortex.
It also plays a role in "match/mismatch" computations: a comparison between sensor input and expected/stored representations.

Functional Synthesis Summary

Diagram highlighting the interaction of these distinct pathways to generate and recall memories.

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Description

This quiz explores the intricacies of the CA3 region of the hippocampus and its role in memory encoding, as well as the interactions within the hippocampal structure. Delve into the mechanisms behind memory retrieval and the specific functions of the mossy fibers. Test your understanding of the anatomical organization of granule and pyramidal cells and their implications in anxiety and memory processes.