Midterm Exam Study Guide

dendrite definition

primary receptive zone for input; receive chemical signals (neurotransmitters)

nucleus (neuron) definition

contain’s cell’s genetic material and nucleolus; regulates gene expression, protein synthesis, and cell maintenance

cell body/soma definition

central part that contains nucleus and essential organelles

axon definition

conducts electrical impulses (action potentials) away from the cell body/soma toward other neurons, muscles, or glands

myelin sheath definition

insulating layer that significantly increases the speed and efficiency of nerve impulse conduction while preventing signal decay

node of Ranvier definition

small gaps in myelin sheath, containing high concentrations of voltage-gated Na channels, allowing action potential to “jump” between nodes via saltatory conduction, significantly speeding up electrical impulse propagation along the nerve fiber

axon terminal definition

converts electrical signals (action potentials) into chemical messages (neurotransmitters), which are stored in synaptic vesicles

synapse definition

junction between neurons that allow them to communicate with one another

occipitoparietal pathway definition

where/how (dorsal) stream; V1, V2, V3, MT/V5, posterior parietal cortex; used for spatial localization, motion perception, visually guided actions, etc.

receptive field definition

specific region of sensory space (e.g., a spot on the retina, a patch of skin, etc.) that alters the firing rate of the neuron when stimulated; defines the spatial, temporal, or feature-based selectivity of the neuron

hierarchical organization of visual areas:

• primary visual cortex (V1): receives input from lateral geniculate nucleus (LGN) of thalamus; neurons respond to basic features such as orientation, edges, and spatial location

• secondary visual cortex (V2): processes more complex combinations of features, such as contours and binocular disparity

• visual area 3 (V3): involved in dynamic form and motion processing

• visual area 4 (V4): involved in color perception and object features

• middle temporal visual area (MT): specialized for motion perception

major visual processing streams

• ventral stream (”what”): V1 → inferior longitudinal fasciculus → inferior temporal cortex

• dorsal stream (”where”): V1 → posterior parietal cortex → superior longitudinal fasciculus

how visual areas are identified

retinotopic mapping, cytoarchitecture, functional selectivity, neuroimaging and electrophysiology (e.g., fMRI, single-cell recordings, lesion studies, etc.)

retinotopic mapping definition

visual areas preserve a map of the visual field; adjacent neurons represent adjacent locations in visual space

cytoarchitecture definition

different areas have distinct cellular structures and layer patterns

functional selectivity definition

neurons in each area respond preferentially to specific visual features (e.g., orientation, motion, color, etc.)

key functional properties of visual cortex

retinotopy, feature selectivity, columnar organization, increasing receptive field size (as processing moves from early to higher visual areas), parallel processing

parallel processing definition

multiple visual attributes (color, motion, form, etc.) are processed simultaneously in different pathways

define visual illusions and describe how they are used to tease out a visual area’s role in perception

• occur when perception differs from the physical properties of the stimulus

  • neural responses are measured to see which brain areas reflect the perceived interpretation rather than the physical stimulus

define ambiguous stimuli and describe how they are used to tease out a visual area’s role in perception

• can be interpreted in multiple ways while the physical image remains unchanged

  • researchers examine which brain areas change activity when perception switches

  • ex: face-vase illusions

define feature manipulation experiments and describe how they are used to tease out a visual area’s role in perception

• researchers systematically manipulate visual features (motion, color, shape) while recording neural responses to determine feature specialization

  • ex: moving dot patterns strongly activate MT area

patient DF

unable to recognize common objects/pictures by sight, specifically reporting object orientation/width, but able to interact with environment/objects as needed

apperceptive agnosia definition

functionally blind; early visual processing intact, but impaired feature extraction; includes impaired figure-ground separation, integrative agnosia

integrative agnosia definition

relatively normal visual processing of color, illumination, light, etc., but impaired shape processing (forms)

associative agnosia definition

normal visual processing but failure to render meaning; confirmed by matching-by-function test; includes prosopagnosia

Snellen Chart definition

neuropsychological test that measures visual acuity/clarity

Humphrey Visual Field Test definition

neuropsychological test that assesses visual field deficits

Birmingham Object Recognition Battery definition

neuropsychological test that evaluates visual object recognition and helps diagnose visual agnosia

Benton Facial Recognition Test definition

neuropsychological test that tests face perception abilities, often used to assess prosopagnosia

MOCA definition

neuropsychological test for visuospatial/executive function, naming, attention, language, abstraction, delayed recall, and orientation; detects mild cognitive impairment and early dementia

methodological considerations that impact scientific quality of patient studies

• premorbid functioning → baseline?

• control groups → healthy group? or group with damage in another area?

• etiology → consequences of different injuries?

• neuropsychological screening → multiple tasks needed

• statistical power → how to get generalized results?

surgical extirpation definition

irreversible cut/vacuuming of tissue of interest

electrical lesions definition

irreversible heating of tissue with strong electrical current

chemical lesions definition

injection of neurotoxins; can be reversible (i.e., lidocaine) or irreversible (i.e., ibotenic acid)

croygenic lesions definition

reversible freezing of brain tissue

single dissociation definition and disadvantages

• damage to region A leads to impaired function X but does not impair function Y

• cannot reveal whether function X is truly independent; it may just be harder than function Y or share a partial neural base

• cannot confirm whether the damaged region is the only structure responsible for the function

double dissociation definition, advantages, and disadvantages

• damage to region A is dissociated from function Y, damage to region B is dissociated from function X

• provides strong evidence for independent, modular brain functions

• cannot be explained by one task being harder than the other

• extremely difficult to find patients with precise, complementary lesions/damage

• functions may not be entirely independent, but may still share some underlying, partially dependent, or overlapping neural resources

according to Vaidya et al., why might permanent and reversible lesions not always yield converging results?

• compensation and neural reorganization (neuroplasticity) after permanent lesions

• permanent lesion may trigger plastic changes across distributed networks (e.g., strengthening alternative pathways), while reversible manipulations typically do not induce the same large-scale plasticity, and may show stronger or different deficits

• reversible techniques do not perfectly mimic the absence of neurons; some neural activity may remain or the manipulation may effect specific cells types or signals differently than a lesion

patient LJ

stroke patient with severe right hemisphere damage leading to severe left spatial neglect

spatial neglect definition

failure to report/respond/orient to stimuli on contralesional side (usually left side after right hemi damage); multimodal neglect; biased spatial attention

• not due to primary sensory/motor loss

• deficit appears across many tasks (e.g., visual search, line bisection, cancellation tasks, mental imagery, etc.)

• reduced activity leads to diaschisis (inactivity in regions that are neuronally connected to the damaged right hemisphere)

dorsal attention network (DAN) definition

top-down, goal-directed endogenous attention control (bilateral)

• related areas: intraparietal sulcus, frontal eye fields

ventral attention network (VAN) definition, lateralization, and related areas

bottom-up stimulus-driven attention capture/reorienting (strongly right-lateralized)

• related areas: tempoparietal junction, ventral frontal cortex

biased competition model of attention definition

if competing stimuli are placed within the preferred area of a neuron, the firing rate decreases; attention biases competition (directing/prompting makes stimuli more salient)

brain bases (related regions) of spatial neglect

• inferior parietal lobule (IPL)

• tempoparietal junction (TPJ)

• superior temporal gyrus and inferior frontal gyrus

• subcortical areas (basal ganglia, thalamus)

Posner spatial cueing task definition

arrow on screen leads/misleads/remains neutral for the viewer to target stimulus; measures reaction times

how to interpret findings from Postner cueing task

• faster responses on avlid trails than neutral trials → “benefit of attention”

• slower responses on invalid trials than neutral trials → “cost of reorienting”

• large invalid cue cost → difficulty disengaging/reorienting attention

• reduce/absent valid cue benefit → difficulty voluntarily orienting attention to cued location

• strong asymmetry between left and right targets → indicates spatial neglects or lateralized attention deficits

Posner spatial cueing task in patients with spatial neglect (Corbetta & Shulman article)

• target detection fastest when presented ipsilesionally and validly cued

• patients still benefit from cueing in the contralesional side when there is no competing stimuli

• patients are faster to detect a validly cued contralesional target than an invalidly cued contralesional target

scalp electroencephalography (EEG) definition, advantages, and disadvantages

measurement of electrical activity from large populations of cortical neurons via electrodes on the scalp

• advantages: high temporal resolution (ms), noninvasive, relatively low cost, widely available, good for studying timing of cognitive processes

• disadvantages: poor spatial resolution (signal distortion), hard to localize exact brain sources, sensitive to noise, unable to detect activity from deeper structures

magnetoencephalography (MEG) definition, advantages, and disadvantages

measures magnetic fields produced by neural electrical currents

• advantages: high temporal resolution (ms), better spatial localization than EEG (magnetic fields less distorted by the skull/cap), noninvasive

• disadvantages: expensive equipment, requires shielded rooms, not sensitive to deeper brain structures, orientation of neurons affects detectability

intracranial EEG (iEEG/ECoG) definition, advantages, and disadvantages

measures electrical activity recorded directly form electrodes placed on or in the brain

• advantages: high temporal resolution (ms), better spatial resolution, high signal-to-noise ratio (electrodes are close to neurons), can record high-frequency activity, allows electrical stimulation mapping to test causal roles of brain regions

• disadvantages: highly invasive, only possible in clinical patients, limited electrode coverage determined by clinical needs (not research design), small sample sizes

single-neuron (single-unit) recordings definition, advantages, and disadvantages

measures action potentials from individual neurons using microelectrodes

• advantages: highest spatial precision, allows study of neural coding and tuning properties, extremely precise temporal resolution

• disadvantages: very invasive, rare in humans, records only a tiny number of neurons (limits generalization)

unique benefits of invasive human recordings

• direct measurement of neural activity

• millisecond timing + millimeter spatial precision

• ability to stimulate brain regions and observe behavioral effects

• opportunity to study human cognition directly, avoiding cross-species inference

unique challenges of invasive human recordings

• ethical constraints; recordings done only for clinical reasons

• electrode placement is clinically determined → uneven sampling

• patients may have neurological conditions that can affect results

• limited experimental time during hospital monitoring

postsynaptic potentials definition

small changes in membrane voltage in the postsynaptic neuron; can be excitatory or inhibitory; decreases with distance; determines whether the neuron reaches firing threshold

action potential definition

large, rapid electrical spike that travels down the axon/hillcock; all-or-none signal; regenerates and travels long distances without weakening

event-related potentials (ERPs) definition

voltage changes in EEG that are time-locked to a specific sensory, cognitive, or motor event; obtained via averaging the repeated trails of EEG recordings to cancel random background noise; signal is segmented into short time windows around each event

how are ERPs interpreted and analyzed?

interpreted through components, defined by their polarity, timing, and scalp distribution

• ex: N170 (negative voltage, peak occurs about 170 ms after stimulus) → linked to early face perception, strongest over occipitotemporal scalp electrodes

• analyzed by measuring amplitude, latency (timing), topography (distribution across electrodes)

primary currents definition

intracellular currents generated by neural activity; occur in large, synchronously active populations of neurons; main source of magnetic fields measured by MEG

secondary currents definition

currents that arise when primary currents create voltage differences that drive passive current flow through surrounding tissue; spread through conductive extracellular tissue; contribute strongly to electric potentials measured by EEG

dorsolateral PFC functions

working memory, executive control, planning and problem solving, cognitive flexibility, top-down control of attention, complex reasoning

ventrolateral PFC functions

response inhibition, selection among competing representations, language-related processing, cognitive control of memory retrieval

orbitofrontal cortex (OFC) functions

reward and punishment evaluation, decision-making based on value, emotional regulation, adaptive learning from feedback

medial PFC functions

self-referential processing, social cognition, emotion regulation, motivation and value representation

cognitive control definition

ability to guide behavior according to goals, especially when habits must be overridden, distractions exist, multiple responses compete, etc.

role of PFC in cognitive control

PFC actively maintains representations of context (goals, rules, task demands), signaling bias in other brain systems (i.e., perception, memory), and ensuring the correct response wins the competition; active maintenance of context to bias processing

patient WR

bilateral lesions in dorsolateral PFC; basic abilities remained intact (normal IQ, perception, memory tests); severely impaired real-world behaviors; struggled with novel/unstructured situations

• able to perform simple instructions and perform routine tasks

• failed when tasks require planning/prioritizing, distractions were present, rules changed, etc.

• contextually inappropriate behavior (i.e., laughing during a funeral)

constituent process of cognitive control (list)

inhibitory control, working memory updating, cognitive flexibility, conflict monitoring, sustained/goal maintenance, etc.

inhibitory control definition and related lab tasks

ability to suppress automatic or prepotent responses

• lab tasks: Stroop task, stop-signal task, go/no-go task

working memory updating definition and related lab tasks

maintaining and updating task-relevant information

• lab tasks: N-back task, digit span task

cognitive flexibility definition and related lab tasks

ability to shift between different rules or task sets; multitasking

• lab tasks: task switching paradigm, Wisconsin card sorting test

conflict monitoring definition and related lab tasks

detecting when competing responses of information are present

• lab tasks: Eriksen flanker task, Stroop task

sustained/goal maintenance definition and related lab tasks

ability to maintain goals over time and resist distraction

• lab tasks: continuous performance task

excitatory neurotransmitter definition and examples

chemical messengers that stimulate the brain by increasing the likelihood that a target neuron will fire an action potential

examples: noradrenaline, dopamine, glutamate, serotonin, histamine, acetylcholine, etc.

inhibitory neurotransmitter definition and examples

chemical messengers that reduce the likelihood of a neuron firing an action potential by hyperpolarizing the postsynaptic membrane

examples: GABA, glycine, etc.

how neurotransmitters are identified (characteristics)

• presence in the presynaptic neuron

• release upon stimulation of neuron

• specific postsynaptic effect

• specific receptors on the postsynaptic cell

• mechanism for removal of neurotransmitter (i.e., enzymatic breakdown, reuptake, diffusion)

ionic dynamics of synaptic release

1. arrival of an action potential

2. membrane depolarization

3. opening of voltage-gated Ca2+ channels

4. calcium influx into terminal

5. vesicle fuses with membrane via proteins

6. neurotransmitter release into synaptic cleft via exocytosis

7. postsynaptic receptor activation; ion channels opened

how neurotransmitter signaling stops

• reuptake: neurotransmitters are transported back into presynaptic terminals via specific transporter proteins

• enzymatic breakdown

• diffusion away from synapse: neurotransmitters diffuse out of synaptic cleft, reducing local concentration

• desensitization/receptor internalization: postsynaptic receptors may become less responsive or removed from the membrane after prolonged stimulation

agonist definition

bind to and activate a receptor, mimicking the endogenous action of a neurotransmitter

antagonist definition

bind to and block a receptor, preventing a neurotransmitter from activating it

reuptake inhibitors definition

increases extracellular neurotransmitter levels by blocking reuptake into presynaptic neuron (e.g., SSRIs)

enzyme inhibitors definition

binds to an enzyme and decreases its activity, slowing or stopping necessary metabolic reactions

advantages of perturbing brain function via exogenous drug administration

• helps determine how specific neurotransmitters contribute to behavior/cognition (causal inference)

• clinical relevance

• can affect distributed circuits in ways that focal lesions cannot

disadvantages of perturbing brain function via exogenous drug administration

• poor spatial specificity (can affect many brain regions)

• temporal limitations (effects may last hours/days)

• off-target side effects

• compensatory mechanisms (brain can adapt, masking drug effects)

translational logic of drug discovery (Robbins article)

• cross-species tasks allow for identifying pharmacological effects in humans, to then be examined more deeply and invasively in animal models

• goal: push evidence-based therapeutics onto the market (most remain serendipitous!)

• important to develop more precision in pharmacological interventions

  • most remain fairly nonspecific, often with side effects or abuse potential that raise cost

  • ex: atomoxetine is not as effective as stimulants, but does not have abuse potential or as many unwanted side effects

key pharmacological findings regarding PFC functioning (Robbins article)

• dopamine (in moderation) improves working memory and cognitive control

• noradrenaline supporting attention, vigilance, and goal maintenance; manipulated by drugs like atomoxetine to enhance PFC function

• acetylcholine enhances signal detection and attentional focus in PFC-dependent tasks

• serotonin (5-HT) modulates impulsivity and affective regulation, particularly via orbitofrontal regions

• pharmacological manipulations in humans (e.g., dopamine agonists) modulate PFC-dependent tasks