Explaining Capgras Syndrome: Lecture Notes PDF

Explaining Capgras Syndrome - Believed parents were imposters - Sometimes believed he himself was an imposter - Didn’t believe he was actually living in his own home even though he was Capgras Syndrome - Patients can recognize loved ones, but patients think they are actually impo...

Explaining Capgras Syndrome - Believed parents were imposters - Sometimes believed he himself was an imposter - Didn’t believe he was actually living in his own home even though he was Capgras Syndrome - Patients can recognize loved ones, but patients think they are actually imposters - Think real loved one was kidnapped (or worse) - May even see slight differences between real loved one and “imposter” - Normal recognition of face/other familiar objects involves two systems 1. Cognitive appraisal 2. Emotional appraisal - In Capgras syndrome, these two processes are disconnected - Note: viral infections (ie. syphillis) can cause same effects What Do We Learn From Capgras Syndrome? - Simple cognitive processes involve multiple brain regions a) Ex. frontal cortex and retrosplenial cortex, after sensory areas - Sub-processes, such as emotional and cognitive aspects of recognition, must be assembled or connected Organization of Brain and its Functions Neurons and Glia - Basic parts of a neuron a) Dendrites: detect incoming signals from other neurons b) Cell body: contains nucleus and cellular machinery c) Axon: transmits signals to other neurons - Glia: support neuronal functions Synapse - Gap between neurons - Neurotransmitters bind to receptors in postsynaptic membrane - If sufficient ionic flow to surpass cell’s threshold, action potential produced - All-or-none law: action potential always of same magnitude - When action potential generated, neuron “fired” or “activated” - Stronger response = more action potentials within 1s - Synaptic transmission a) Allows neuron to receive and integrate information from many other neurons b) Strengths of synaptic connections are adjustable, temporarily or for long term, by experience 3 Main Brain Structures 1. Hindbrain 2. Midbrain 3. Forebrain Hindbrain - Top of spinal cord - Key life functions - Cerebellum: largest region of hindbrain, movements and balance (spatial learning) - Reticular activating system a) Pons: level of arousal b) Medulla (oblongata): vital processes (heart rate, breathing, blood pressure, reflexes) Midbrain - Coordinating precise eye movements - Relaying auditory information from ears to forebrain - Regulating pain experiences Forebrain - Surrounds midbrain and most of hindbrain - Includes cerebral cortex (80% of brain) and subcortical structures - Two hemispheres, longitudinal fissure in middle Subcortical Structures (of Forebrain) - Thalamus: sensory relay station - Hypothalamus: controls behaviours that serve specific biological needs (4 F’s) - Limbic system a) Amygdala: emotional processing b) Hippocampus: learning and memory Cerebral Cortex - Largest portion of human brain, “neocortex” - Thin layer of tissue covering cerebrum (forebrain) - Regions of cortex a) Sensory areas b) Motor areas c) Association areas Sensory Areas - Primary somatosensory area: skin sensations - Primary auditory cortex: auditory sensations - Primary visual cortex: vision a) Contralateral organization (ex. Right visual field controlled by left V1) b) Cortical space assigned based on acuity (ex. V1, S1) Motor Areas - Primary motor cortex (M1): output to spinal cord and then muscle groups, somatosensory movements - Secondary motor cortex (premotor and supplementary motor areas): selecting motor programs based on stimuli or memory - Contralateral control - More cortical coverage reflects greater motor precision Some Organizing Principles - Parallel pathways in each sensory modality - Serial, or hierarchical processing of information - Functionally related cortical areas lie close together Research Methods Sources of Evidence about the Brain - Cognitive neuroscience relies on variety of methods to study brain/nervous system - Neuropsychology - Neuroimaging - Electrical recordings - Optical imaging (2-photon fluorescent imaging: animal studies only) - Manipulation of brain function Data from Neuropsychology - Neuropsychology: study of brain’s structures and their relation to function - Clinical neuropsychology: functional loss following brain damage (lesions) Data from Neuroimaging - Structural neuroimaging techniques a) Computerized axial tomography (CT) scans b) Magnetic resonance imaging (MRI) scans - Functional neuroimaging techniques a) Positron emission tomography (PET) scans b) Functional magnetic resonance imaging (fMRI) scans Data from Electrical Recording - Extracellular recording with depth electrodes (or arrays) a) Recording action potential and local field potentials (mainly summation of synaptic currents) b) Used to study how individual neurons and local circuits encode information c) Can be done with conscious patients (ex. In prep for neurosurgery for removing locus of intractable epilepsy) - Electroencephalogram (EEG) a) Aggregated signals from very large population of neurons b) Used to study - Broad rhythms (ex. Sleep stages) - Event-related potentials (ERPs) c) Remains essential for epilepsy models (ex. Portable system worn for 2 weeks) d) Non-invasive e) Great for wireless transmission of signals - Electrocorticography (ECoG) a) Aggregated signals from very large population of neurons  b) Can be done on conscious patients (ex. In prep for neurosurgery for removing locus of intractable epilepsy, done before any depth recording and after EEG) ECoG and EEG: Macroscopic Data - ECoG vs. LFP: signal loss due to cortical layers, CSF, pia and arachnoid maters - ECoG vs. LFP: more “spatial averaging”, less high frequency info than LFP - ECoG retains more info than EEG due to low conductivity of bone Manipulations of Brain Function - Brain function can also be studied through techniques that manipulate its functions - Chemical effects on neurotransmitters/receptor systems - Electrical/magnetic stimulation - Gene manipulation (animal studies only), gene therapy (humans) - Ethical considerations (institutional review boards) Combining Techniques - Necessity: to understand how cognition works, we must record both poeple/animals’ behavioural performance as well as their brain signals - Every method has strengths and weaknesses a) EEG - Strength: temporarily locating neural activity (when?) - Weakness: spatially locating neural activity (where?) b) fMRI scans - Strength: spatially locating neural activity (where?) - Weakness: temporarily locating neural activity (when?) c) MRI scans: detect brain structures, not activity - Researchers can overcome limitations by combining techniques - Problem: most neuroimaging techniques used to study brain activity and structures provide only correlational data - Sources of causal data a) Brain lesions (neuropsychological studies) b) Transcranial magnetic stimulation (TMS) - Magnetic pulses activate or inhibit neurons - Produces temporary lesions c) Microstimulation in conscious patients undergoing neurosurgery Textbook Notes Capgras Syndrome - Rare disorder where individuals recongize familiar people but believe they have been replaced by imposters - Symptoms a) Patients identify faces accurately but feel no emotional connection b) May believe loved ones have been replaced by robots or lookalikes c) Can lead to paranoia and (sometimes) violent behaviour - Two pathways in face recognition 1. Cognitive appraisal system: recognizes physical features and identifies faces 2. Emotional appraisal system: links faces to emotional responses - In Capgras syndrome, emotional appraisal system damaged, leading to lack of familiarity and emotional warmth - Brain regions affected a) Amygdala (temporal lobe) damage - Evaluates emotional significance of stimuli - Damage leads to lack of emotional response to familiar faces b) Prefrontal cortex damage - Normally helps distinguish reality from delusions - Damage leads to difficulty in logical reasoning, resulting in paranoid beliefs - MRI and fMRI scans show a) Temporal lobe abnormalities (linked to amygdala dysfunction) b) Frontal lobe dysfunction (affecting reasoning and judgement) What Capgras Syndrome Teaches About Brain - Face recognition not single process but involves multiple brain regions - Brain integrates rational thought and emotional evaluation - Brain damage can disrupt reality perception and create delusions Hindbrain (Basic Life Functions) - Medulla: controls breathing, heart rate, and digestion - Pons: connects brainstem to cerebellum - Cerebellum: coordinates movement, balance and spatial reasoning Midbrain (Relay and Coordination Center) - Regulates eye movement and auditory processing - Plays role in pain perception Forebrain (Congitive and Emotional Processing) - Cerebral cortex: outermost layer, responsible for complex thinking - Subcortical structures a) Thalamus: relays sensory signals b) Hypothalamus: regulates hunger, thirst and hormones c) Limbic system (includes amygdala and hippocampus): crucial for emotion and memory Cerebral Cortex - Frontal lobe: planning, reasoning and movement (motor cortex) - Parietal lobe: sensory information, spatial awareness - temporal lobe: auditory processing, memory (hippocampus), emotions (amygdala) - occipital lobe: visual processing Brain Hemispheres and Lateralization - Brain has two hemispheres connected by corpus callosum - Left hemisphere: language, logic and analytical thinking - Right hemisphere: spatial reasoning, facial recognition, emotions - Split-brain studies: patients with severed corpus callosum show differences in perception and motor control Neuroimaging Techniques - Structural imaging: shows brain anatomy a) MRI: high-resolution images b) CT scan: X-ray based 3D images - Functional imaging: shows brain activity a) fMRI: measures blood flow, indicating active areas b) PET scan: tracks glucose metabolism - Electrical recording a) EEG: measures electrical activity in brain b) ERPs: tracks brain responses to stimuli - Brain stimulation a) TMS: temporarily disrupts brain function to study specific regions Neuron Strucutre - Dendrites: receive signals from other neurons - Cell body (soma): processes signal - Axon: tansmits electrical impulses - Synapse: gap between neurons where communication occurs Synaptic Transmission - Neurons communicate through neurotransmitters - Types of neurotransmitters a) Dopamine: motivation, pleasure b) Serotonin: mood regulation c) Acetylcholine: muscle movement d) Glutamate and GABA: excitatory and inhibitory signals - Myelin sheath: insulates axons and speeds up signals Motor Cortex (Frontal Lobe) - Controls voluntary movements - Organized in map-like structure Sensory Cortex (Parietal Lobe) - Processes touch, pain and temperature - Also follows map-like organization Association Areas - Handle higher-order functions like problem-solving, memory and attention - Damage can result in agnosia (inability to recognize objects) or neglect syndrome (ignoring one side of body) Brain Disorders and Deficits - Aphasia: language impairment due to damage in a) Broca’s area (frontal lobe): difficulty producing speech b) Wenicke’s area (temporal lobe): difficulty understanding speech - Agnosia: inability to recongize objects or faces a) Visual agnosia: can’t recognize objects visually but can by touch b) Auditory agnosia: can’t recognize sounds - Neglect syndrom: ignoring one side of visual field due to parietal lobe damage - Apraxia: difficulty with motor planning Brain Plasticity and Learning - Brain can rewire itself based on experience - Synaptic plasticity: learning strengthens or weakens neural connections - Neurogenesis: new neurons can form in specific brain regions