Cognitive Neuroscience Exam Notes

Patient Studies & Lesion Method

• Major source of knowledge about brain and mind through trauma, stroke, tumor, degenerative diseases, epilepsy, and neurosurgery.

• Neuropsychological deficits include agnosia (recognition loss), aphasia (language loss), apraxia (action disorders), amnesia (memory loss), and ataxia (poor coordination).

• Agnosia subtypes: visual, form, finger, simultanagnosia, associative, apperceptive, prosopagnosia.

Dissociating Cognitive Functions

• Cognitive functions and brain regions can be dissociated through selective impairment.

• Requires comparing patient/control groups on at least two tasks to show specific deficits.

Single Dissociation

• Patient group performs poorly on one task but is spared on another, suggesting involvement of a brain region in one cognitive function.

• Limitation: Doesn't exclude the region's involvement in other functions; poor performance may be due to other factors.

• Example: Temporal lobe damage affecting declarative memory.

Double Dissociation

• Stronger evidence for separation of cognitive functions, involving two patient groups with complementary deficits.

• Patient group 1: Impaired on task X, spared on task Y.

• Patient group 2: Impaired on task Y, spared on task X.

• Demonstrates distinct brain regions associated with different tasks.

Limitations of Patient Studies

• Assumption of modularity may not hold due to brain plasticity.

• Lesions are often extensive and varied, affecting multiple functional centers.

• Lesion anatomy can be inaccurate, not considering connections.

• Individual differences in functional anatomy exist.

• Poor temporal resolution limits inferences about processing stages.

Benefits of Patient Studies

• Show necessary areas for cognitive functions (double dissociation).

• Reveal cognitive, emotional, and social consequences of deficits.

• Cost- and time-effective, with possible single-case studies.

• Can be done with control groups to limit criticism.

fMRI

Physics

• Uses magnetic field (B_0) and radio energy to produce an image.

• Aligns nuclei with a net magnetic moment within the field.

• Nuclei absorb and re-emit radio frequency energy.

Image Acquisition

• Nuclei spin around the main magnetic field.

• RF pulse tips magnetization ( M ) out of alignment with B_0.

• M gradually returns to alignment, and spins lose phase coherence.

• These changes are detected as the ‘MRI signal’.

BOLD Response

• Based on relative levels of de/oxyhemoglobin changing from cortical activity.

• Initial dip: momentary decrease in blood oxygenation after neural activity increases.

• Blood flow increases, overcompensates, peaks around 6 seconds, then falls back, often with an undershoot.

• De/oxyhemoglobin have different magnetic properties affecting local signal strength.

Cognitive Subtraction

• Compares reaction times between two tasks, one with the same components as the other plus the process of interest.

• Assumption of pure insertion: Component processes can be added without disrupting others.

Experimental Designs

• Block Design: Alternating blocks of task and rest.

• Event-Related: Allows (pseudo)random stimulus presentation and retrospective coding.

fMRI Preprocessing and Analysis

• Steps: Model building, realignment & motion correction, smoothing, normalization, parameter estimation, statistical parametric mapping, contrasts.

• Analysis done independently at every voxel.

Interpreting Blobs

• Clusters of significant statistics show areas where signal change was significantly predicted by the model.

• Changes in signal are due to regional hemodynamics, distantly related to underlying neurological events.

New Directions in fMRI

• Functional-connectivity analyses: calculate correlations between activations in different areas.

• Dynamic causal modelling: explicit models of distributed networks are tested.

Pioneers of Neuroscience

• Von Helmholtz: Measured axon potential speed, refuted vitalism.

• Golgi: Invented silver nitrate staining; debated neuron doctrine.

• Cajal: Used Golgi's method, discovered synapse, supported neuron doctrine.

• Hebb: Proposed cell assemblies as cognition elements.

Neurons

• Cell Body (Soma): Contains nucleus, mitochondria.

• Processes: Dendrites, Axon (with myelin sheath), Terminal buttons.

Supporting Cells - Neuroglia

• Glia Cells: Astrocytes, Oligodendrocytes.

• Peripheral Nervous System (PNS): Schwann cells.

How Neurons Work: Membrane Potential and Ion Exchange

• Resting Potential: Charge across the neural membrane at rest (-70mV).

• Sodium ions (Na^+) must be kept at a greater concentration outside the cell, maintained by ion concentration differences and the sodium-potassium pump.

• The sodium-potassium pump exchanges 3 Na^+ for 2 K^+ ions.

Depolarization and the Action Potential

• Excitation (synaptic) from other neurons raises the membrane resting potential.

• When depolarization reaches a threshold, an action potential is triggered.

• Depolarization occurs locally and spreads down the axon in an all-or-none fashion.

The Synapse

• Pre- and post-synaptic membranes are separated by the synaptic cleft.

• Synaptic vesicles contain neurotransmitter molecules.

• Action potential (AP) triggers neurotransmitter release into the cleft.

Neural Transmission

• Neurotransmitter binds to a receptor, opening ion channels and altering the postsynaptic membrane's polarization.

Excitatory and Inhibitory Post-Synaptic Potentials

• Na^+ channels open → depolarization → EPSP.

• K^+ channels open → hyperpolarization → IPSP.

Neurotransmitters

• Glutamate: Primary excitatory transmitter.

• GABA: Primary inhibitory transmitter
  *Dopamine: Modulates activity in striate, limbic, and cortical areas.

Drugs and the Brain

• Agonists: Facilitate post-synaptic effects.

• Antagonists: Inhibit post-synaptic effects.

Learning

• Classical Conditioning: Associating two stimuli and an automatic response.

• Instrumental / Operant Conditioning: Associating a learned response and a stimulus

Memory

• Hebb’s Rule: A synapse repeatedly active when the postsynaptic neuron is firing will be strengthened.

• Classical Conditioning: US (puff) → UR via strong synapse. Pairing tone with US strengthens weak synapse.

Hippocampus and Memory Consolidation

• Amnesia: A deficit in memory resulting from brain damage

• Medial Temporal Lobe & Hippocampus.

• ECT: electroconvulsive therapy.

• Case H.M.: Disrupted transfer from short-term to long-term memory → dense anterograde amnesia.

Cellular Basis of Long-Term Learning: Long-Term Potentiation (LTP)

• Principle: If a weak and a strong input act on a neuron simultaneously, the weak synapse becomes stronger (Hebbian learning).

• Low-frequency stimulation of a synapse or firing of two inputs out of phase results in its weakening.

Attention

Involves preferential treatment / selection of a subset of information.

Theories of Attention: Selective Attending

Broadbent’s (1958) model (B&C p306 on). Top-down selection of relevant inputs at an early stage of processing.

Attention in Space

Early selective attenuation of information from visual cueing of spatial locations. Posner’s cueing paradigm

Voluntary and Reflexive Orienting

Central, symbolic, cues evoke voluntary shifts of attention. Peripheral, non-symbolic, cues evoke reflexive shifts of attention

Attention to Objects

Can also be ‘object based’. Objects can influence the orienting of attention in response to cues

Disorders of Attention

Hemispatial neglect. Usually results from right parietal damage

Brain Mechanisms of Attention

Attentional control and amplification of widespread processing. Multiple regions activated in fMRI studies of attentional orienting

Brain Mechanisms: Attentional Networks

Alerting - maintaining a high state of sensitivity to incoming stimuli. Orienting - attending to the source of a sensory signal. Executive - directs attention according to an individual’s goals

Executive Functions

Provide organization and order to our actions and behavior. Govern cognitive, linguistic, and motor domains

Include: Representing and maintaining goals, planning for the future, inhibiting or delaying responding

Paradigm for Testing

Working memory and set-shifting, sensory attentional filtering, impulse/response control and goal-directed behavior, conflict resolution, decision-making

PFC Damage

Dorsolateral lesions lead to frontal executive syndrome. Ventromedial damage can lead to problems with emotional control

Goal-Oriented Behavior

Patients with frontal brain damage have problems with everyday life. Planning involves creating a hierarchy of goals and subgoals

Staying on Track

As task difficulty increases, the Anterior Cingulate (AC) gyrus becomes increasingly active

Error Detection and Avoidance

Detecting errors – the Error-Related Negativity
Avoiding errors – AC activation is greater when people do tasks that elicit errors

vmPFC Damage

Lesions to vmPFC often result in: Reduced inhibition of affect – rude and hostile. Deficits in reversal learning, (reverse learned response). Myopia for the future (impulsivity)

Summary: Executive Functions Involve

Inhibition, planning, working memory, self-monitoring, response selection, motor control, regulation of emotion, motivation

Anatomical Asymmetry

Anterior right hemisphere and posterior left hemisphere overlap midline. Sylvian Fissure – ascends more anteriorly in the right hemisphere, longer in the left hemisphere

Planum Temporale

Wernicke's area. Anatomical Asymmetry

Auditory Processing

Left auditory cortex. Planum temporale. Right auditory cortex

Testing Each Hemisphere

Historically, unilateral brain damage has revealed much about cerebral asymmetry. Newer techniques also are revealing

Visual input is predominantly Contralateral. Test each hemisphere using lateralized visual presentation

Hemispheric Connections

Arrangement in rough topography (anterior origin – anterior crossing). Associative cortex connections predominate

Split Brain

Callosotomy - Section of corpus callosum. The Disconnection Syndrome: Prevents spread of seizure activity from one side of the brain to the other, BUT creates “disconnection syndrome”

Historical Views of the Mind and Body

Rene Descartes (1596 - 1650). Formulated ideas on fundamental topics relevant to modern psychology. Central to the development of science of natural processes

Cartesian Dualism

Mind and body are separate realms. Body is an ‘earthen machine’ – banished vital spirits etc (replaced mystical action with mechanical)Mind is essential to our being in a way that body is notDifferent properties – extension vs nonlocalized, deterministic v unboundedExistence of the soul is indubitable

Reject Dualism and take a Monist/Materialist stance

Mind is brain. Psychological phenomena are to be accounted for as the effects of organic changes in the brain and nervous system

Modern perspectives

Awakeness versus sleep. General alertness (versus generally inattentive). Focal attention (versus distraction)

Consciousness & the Brain

Global workspace: Processing of a stimulus may reach consciousness only if it is integrated into a large-scale system of cortical activity .Attentional amplification (Pre-frontal cortex) leads to interaction of modular processes allowing information to be maintained and influence other processes.