Hippocampus: Structure and Function Overview

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Questions and Answers

What type of memory was preserved in Patient H.M. following his surgery?

Semantic memory

Procedural memory (correct)

Episodic memory

Long-term declarative memory

Which of the following functions is NOT associated with the hippocampus?

Emotional regulation (correct)

Context learning and retrieval

Working memory

Spatial learning and navigation

What correlation was found related to taxi drivers and the hippocampus?

Increased cognitive flexibility

Decreased fear response

Decreased spatial awareness

Increased volume of the right posterior hippocampus (correct)

What type of amnesia was specifically highlighted in Patient H.M.'s case?

Global amnesia Signup and view all the answers

In rats, what is the consequence of removing the hippocampus in relation to learned contexts?

Failure to show freezing to shocked contexts Signup and view all the answers

Which study indicated activation in the right hippocampus correlating with context anxiety in humans?

Hasler et al., 1997 Signup and view all the answers

What aspect of memory did hippocampal lesions impair in rats during the radial maze task?

Spatial working memory Signup and view all the answers

What mechanism underlies the transition from normal neuronal firing to seizure activity in the hippocampus?

Failure of post-PDS hyperpolarization Signup and view all the answers

Which of the following accurately describes hypersynchrony in the context of seizures?

Neurons firing together in a specific area Signup and view all the answers

Which brain region is highlighted as being particularly affected in individuals with Alzheimer's disease, especially regarding memory formation?

Entorhinal cortex Signup and view all the answers

In individuals with schizophrenia, what notable change occurs in the hippocampus during memory retrieval tasks?

Failure to recruit the hippocampus Signup and view all the answers

How does hyperexcitability contribute to seizure generation in the hippocampus?

It leads to prolonged bursts of action potentials Signup and view all the answers

Which type of dendrites extends longer in pyramidal neurons?

Apical dendrites Signup and view all the answers

What is the primary role of feed-forward inhibition in CA1 neurons?

To dampen the effect of afferent excitation Signup and view all the answers

Which strata do apical dendrites of pyramidal neurons pass through?

Stratum radiatum, stratum lucidum, stratum lacunosum-molecular Signup and view all the answers

What does the prolonged IPSP following an EPSP indicate?

Coincidence detection capacity Signup and view all the answers

What is primarily recorded when measuring local field potentials in the hippocampus?

Summed electrical activity from multiple cells Signup and view all the answers

What key property does coincidence detection in CA1 neurons facilitate?

High fidelity timing transfer Signup and view all the answers

What type of receptors do interneurons act on during feed-forward inhibition?

GABAA and GABAB Signup and view all the answers

Where do basal dendrites of pyramidal neurons primarily extend?

Stratum oriens Signup and view all the answers

What is a consequence of the narrowing time window created by feed-forward inhibition?

Restricted presynaptic activity triggering action potentials Signup and view all the answers

What is the primary function of the mutual excitation among CA3 neurons?

To create a positive-feedback cycle that can lead to hyperexcitability Signup and view all the answers

Which type of cells do the Oriens-lacunosum moleculare (O–LM) interneurons primarily target?

Distal dendritic sites Signup and view all the answers

What characterizes the Schaffer collateral pathway?

It is one of the most studied pathways due to its synaptic plasticity Signup and view all the answers

What is a consequence of overexcitation in the hippocampus?

Pathological increases in intracellular calcium leading to cell death Signup and view all the answers

What is the main role of GABAergic interneurons in CA3?

To synchronize and provide inhibition to pyramidal cells Signup and view all the answers

What is the relationship between CA3 and contralateral hemisphere neurons?

CA3 neurons have reciprocal projections to contralateral CA3 neurons Signup and view all the answers

How can interneurons in CA3 synchronize their activity?

Through dendritic gap junctions that couple their activity Signup and view all the answers

What is a potential effect of recurrent collateral circuitry in the CA3 region?

Increased vulnerability to overexcitation Signup and view all the answers

What is a key feature of excitatory terminals from the entorhinal cortex (EC) to CA3?

They are confined to synaptic sites on distal dendrites Signup and view all the answers

What characteristic of pyramidal neurons contributes to the reliability of recorded population EPSPs in the hippocampus?

Their unique synaptic input orientation Signup and view all the answers

In which layer would you expect to record a negative going potential when a field electrode is positioned to assess synaptic input?

Stratum radiatum Signup and view all the answers

What does an increase in the amplitude of the fiber-volley indicate during excitatory synaptic activity?

An increase in presynaptic axons activated Signup and view all the answers

What is the relationship between the time course of field potentials and the underlying synaptic currents?

Field potentials have a time course nearly equal to synaptic currents Signup and view all the answers

What occurs if depolarization reaches a threshold in the hipocampal neuronal population?

A population spike is generated Signup and view all the answers

Where is the field electrode positioned to observe a positive going deflection when assessing synaptic inputs?

Near the cell body layer Signup and view all the answers

What effect does current flowing into the dendrites during excitatory synaptic activity have on the neuronal soma?

It induces depolarization towards action potential threshold Signup and view all the answers

Which statement best describes the role of field potentials in the hippocampus?

They are a summation of electrical activity from multiple neurons Signup and view all the answers

What is indicated by a negative going deflection observed in the recording when action potentials are triggered?

Current moving down the axon away from the electrode Signup and view all the answers

What does the symmetrical arrangement of pyramidal neurons in the hippocampus facilitate?

Enhanced reliability of field potentials recordings Signup and view all the answers

What type of amnesia did Patient H.M. experience as a result of his surgery?

Global amnesia Signup and view all the answers

Which function is primarily attributed to the place cells in the hippocampus?

Firing in response to specific locations Signup and view all the answers

In what way does the hippocampus influence the cortico-striatal loop?

By providing limbic information to other brain regions Signup and view all the answers

What has been observed about the volume of the right posterior hippocampus in taxi drivers?

It correlates positively with the length of time spent as a taxi driver Signup and view all the answers

What is the consequence of removing the hippocampus in rats regarding context learning?

Failure to show freezing to previously shock-paired contexts Signup and view all the answers

What was demonstrated by fMRI studies regarding the hippocampus and working memory tasks?

Increased activation during the maintenance phase Signup and view all the answers

Which finding about context anxiety was supported by neuroimaging studies in humans?

Context anxiety correlates with activation in the right hippocampus Signup and view all the answers

What relationship exists between hippocampal disruptions and procedural memory in humans?

Procedural memory remains intact despite hippocampal damage Signup and view all the answers

What occurs when the field electrode is positioned near the cell body layer in the hippocampus?

A positive going deflection is observed initially. Signup and view all the answers

How does the arrangement of pyramidal neurons impact the electrical fields generated by active neurons?

It creates a symmetry that enhances field potential recordings. Signup and view all the answers

What generally characterizes local field potentials recorded from the hippocampus?

They are influenced by the arrangement and synaptic inputs of neurons. Signup and view all the answers

In which layer does a negative going potential primarily flow when an electrode records synaptic input?

Stratum radiatum. Signup and view all the answers

What happens when depolarization reaches a threshold in the hippocampal neuronal population?

Generation of action potentials is triggered. Signup and view all the answers

In what way does current flowing into the dendrites during excitatory synaptic activity affect the neuronal soma?

It causes a potential increase toward the soma. Signup and view all the answers

What is the primary function of basket cells in the dentate gyrus?

Influencing a large number of granule cells Signup and view all the answers

Which statement accurately describes the function of chandelier cells in the dentate gyrus?

They terminate on the axon initial segments of granule cells. Signup and view all the answers

What role do feedback loops involving mossy cells serve in the dentate gyrus?

They provide excitatory input to granule cells in different septotemporal planes. Signup and view all the answers

What characterizes the medial perforant path (MPP) in relation to granule cell synapses?

It synapses more proximal to the granule cell soma. Signup and view all the answers

Which type of interneuron is primarily responsible for synchronous inhibition of pyramidal cells in CA3?

Basket cells Signup and view all the answers

What distinguishes the lateral perforant path (LPP) inputs to CA3 and CA1 from those of the MPP?

They have distinct functional dissociations based on spatial versus object representations. Signup and view all the answers

What is the primary outcome of dendritic gap junctions in CA3 interneurons?

They allow for synchronized activity among interneurons. Signup and view all the answers

What is the main characteristic of the associational/commissural projection in the dentate gyrus?

It targets the molecular layer and provides excitatory input. Signup and view all the answers

What function does the CA3 region of the hippocampus primarily support in encoding memories?

Asymmetrical linking of memories over time Signup and view all the answers

How do the mechanisms of CA3 and DG interact in memory encoding?

They establish reciprocal connections to facilitate memory association Signup and view all the answers

What distinct challenge does heteroassociation present in memory encoding?

It may result in degraded representations of linked memories Signup and view all the answers

Which of the following best describes how the CA3 region functions in memory encoding?

It allows for the linking of memories from different time points Signup and view all the answers

How does the autoassociative mechanism within CA3 contribute to memory retrieval?

It allows partial retrieval when few components of a memory are presented Signup and view all the answers

What impact does synaptic noise have on information stored in the CA3 region?

Leads to inconsistent memory recall patterns Signup and view all the answers

In what way does the DG's recurrent network contribute to memory processes?

It strengthens synaptic patterns associated with temporal sequences Signup and view all the answers

What role do strengthened synaptic links between components of a memory play in recollection?

They facilitate retrieval by creating associations based on familiarity Signup and view all the answers

What condition occurs when the normal post-PDS hyperpolarization fails?

Ictal discharge Signup and view all the answers

Which of the following describes hyperexcitability in the context of seizures?

Reduced threshold for neuronal firing Signup and view all the answers

How do seizures spread from their origin in the brain?

By synchronizing with neighboring neurons Signup and view all the answers

What characterizes a tonic-clonic seizure?

Uncontrollable muscle contractions Signup and view all the answers

Which brain region is indicated as particularly affected in schizophrenia regarding memory retrieval tasks?

Hippocampus Signup and view all the answers

What impact does the entorhinal cortex have in the context of Alzheimer's disease?

It is one of the first areas affected by Alzheimer's pathology. Signup and view all the answers

What is the outcome of prolonged bursting of glutamatergic neurons in the hippocampus?

Seizure generation Signup and view all the answers

What effect does hippocampal volume reduction have on individuals with schizophrenia?

Impaired memory retrieval Signup and view all the answers

What role does the DG (dentate gyrus) play when it is autoassociative and reciprocal communication is allowed?

It corrects degraded memories for CA3 during transmission. Signup and view all the answers

How does direct perforant path input contribute to the functioning of CA3?

It produces a depolarizing bias that facilitates threshold-reaching input. Signup and view all the answers

What function does the CA1 region serve in relation to the entorhinal cortex?

It decodes and conveys information back to the entorhinal cortex. Signup and view all the answers

What is a potential issue with the function of CA3 when it follows a heteroassociation process alone?

It makes the representation of memories prone to degradation. Signup and view all the answers

What is the significance of CA1 performing a 'match/mismatch' computation?

It compares sensory reality with predictions from DG–CA3 networks. Signup and view all the answers

Study Notes

Hippocampus: A Summary

The hippocampus is one of the most intensively studied structures in the brain.
It's a central component of the Limbic system, along with the amygdala.
Coronal plane views of the hippocampus illustrate its location within the brain.
The hippocampus is a major component of the "affective" cortico-striatal loop, connecting to the ventral striatum and medial prefrontal cortex.
Patient H.M., the most famous case of amnesia, had his hippocampus surgically removed at age 27, to treat seizures.
This surgery resulted in anterograde and retrograde amnesia; unable to form new or recall old declarative memories.
Declarative memories (episodic and semantic) were affected, but procedural memory, language, visuospatial perception, and attention remained.
The length of time spent as a taxi driver correlates with increased volume of the right posterior hippocampus.
"Place cells" in the hippocampus of rodents fire preferentially for certain locations in their environment.
Rats without a hippocampus don't freeze to a context previously paired with shock.
Hippocampal activation was observed in a human PET study of context anxiety.
Hippocampal activation was seen in fMRI studies in humans during the maintenance phase of working memory tasks.
Hippocampal lesions in rats impair their ability to perform spatial working memory tasks.
The anatomy of the medial temporal lobe circuitry shows connections between the entorhinal cortex, hippocampus proper, and subiculum.
The hippocampus proper has a well-defined laminar structure with rows of pyramidal cells.
Transverse slices provide clear visualization of the hippocampal circuitry/lamina.
Overall, hippocampal structure and pathways, plus neuron types like granule cells and pyramidal neurons, are characterized, along with synaptic inputs, responses and functional roles in learning, memory, and spatial navigation.
The hippocampus plays a role in encoding the contextual details of episodic memories.

Hippocampal Disease

The hippocampus is exceptionally vulnerable to diseases like epilepsy, Alzheimer's disease, and schizophrenia.
The hippocampus's high excitability, and recurrent collateral circuitry, make CA3 neurons susceptible to overexcitation, triggering disease-related malfunctions.
Over-stimulation of NMDA receptors leads to excessive intracellular calcium, causing cellular damage (necrosis/apoptosis).
Epilepsy is characterized by hyperexcitability and hypersynchrony of neurons in the brain; the hippocampus is a common origin point for this disorder.
The hippocampus is a critical component for forming and utilizing memories.
Hippocampal volume reduction is observed in individuals with schizophrenia and Alzheimer's disease, affecting memory functions in various ways.
In epilepsy, overexcitation can synchronize activity and spread to other brain areas.

Functional Summary

The hippocampus plays a crucial role in encoding episodic memories, including both the context and the details of an experience.
The hippocampus is involved in pattern separation, allowing the organism to discriminate between similar experiences.
The role of sparse firing in the dentate gyrus (DG) is crucial.
CA3 microcircuits exhibit mutual excitation and contribute to these episodic memories.
CA1 region of the hippocampus acts as a decoder, receiving information from CA3 and sending it back to the entorhinal cortex, playing a crucial part in computations associated with memory recall, and match/mismatch detection.
Pattern completion and recurrent collaterals are involved in these computations.
Perforant pathways connect the entorhinal cortex to the hippocampus, a critical component of the temporal lobe circuitry.
Mossy fibers originate in the dentate gyrus and synapse with CA3 pyramidal cells.
The hippocampus plays a role in the precise temporal sequencing of events.
The hippocampus plays a role in the contextualization/separation of memories.

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Description

Explore the vital role of the hippocampus in the human brain. This quiz delves into its functions within the limbic system, its connection to memory, and significant cases like Patient H.M. Test your knowledge about this critical structure and its influence on learning and memory processes.