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STANFORD / Psychology / PSYCH 50 / What is hemispatial neglect syndrome?

What is hemispatial neglect syndrome?

What is hemispatial neglect syndrome?

Description

School: Stanford University
Department: Psychology
Course: Intro to Cognitive Neuroscience
Professor: Justin gardner
Term: Winter 2016
Tags: Psychology and Cognitive Neuroscience
Cost: 25
Name: Chapters 7 and 13
Description: Week 5 chapters, hopefully the notes will help with the chapter 13 quiz! :)
Uploaded: 02/03/2016
8 Pages 55 Views 6 Unlocks
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Emily Wu


What is hemispatial neglect syndrome?



emilyw12@stanford.edu

Chapter 7: The Control of Attention

Clinical Evidence for Brain Regions Involved in Attentional Control

● hemispatial neglect syndrome: lesions to right inferior parietal lobe, patients tend to ignore stimuli in left visual field (contralateral to side of lesion)

○ can see the stimulus if pointed out, but syndrome seems to be a problem with directing attention to the stimulus

● lesions in right parietal lobe causes impairment in spatial attention to left side ○ lesions in left parietal lobe can cause contralateral impairment too but effects are milder

● Balint’s syndrome: lesions to dorsal posterior parietal and lateral occipital cortex ○ results in simultanagnosia: unable to attend to and perceive more than one visual object at a time


What is mesulam model?



● lesions in superior colliculus in brainstem (generates saccades) slows saccadic eye movement to new stimuli

● Sprague effect: parietal lesion’s effects usually nullified by lesion in superior colliculus ○ theory that hemispatial neglect is due to imbalance of activity of both parietal lobes, but lesion in superior colliculus restores the balance We also discuss several other topics like How are hydrocarbons used in everyday life?

Control of Voluntary Attention

● damage to parietal and frontal cortices disrupt attentional control instead of sensory processing

○ subjects should show change in activity in these areas when doing tasks involving attentional control

● earlier studies used block design because of neuroimaging limitations → later studies were able to use cuing paradigm

○ cuing paradigm benefits: could study the differences in neural activity at time the cue appears and at time the target stimulus appears


What is an easily detected stimuli with a single featural difference?



We also discuss several other topics like What is distance formula and what are its examples?

Single neuron recordings

● studies in nonhuman primates focused on lateral intraparietal area (LIP) and frontal eye fields

● increased neural firing rates in LIP when monkey makes saccade towards target location, covertly directs attention, or delays saccade to location → increased activity attributed to attention allocation to target area

● stimulus salience (how much stimulus stands out from surroundings) determines activity of LIP neurons

○ LIP may have topographically arranged salience map

● premotor theory of attention: shifting attention and preparing goal­directed actions are controlled by shared sensory­motor mechanisms

○ stimulation of specific area in frontal eye fields causes saccades to specific locations

○ conclusion: circuitry responsible for saccades also controls covert visual spatial attention

● temporal sequence of attention: frontal then parietal lobe

Preparatory activation of sensory cortices during attentional control ● when subjects shift attention to a specific area expecting a stimulus to appear, increased activity appears in visual cortex → “preparatory bias” influenced by the frontoparietal cortices

● attention elicits preparatory activity in sensory cortices

Control of Exogenously Induced Changes in Attention

Attentional shifts triggered by sudden stimulus onsets

● temporal sequences of activation of brain areas differ in exogenous cues ○ parietal neurons activated before frontal neurons We also discuss several other topics like Why are discouraged workers not included in the unemployment rate?

○ in endogenous cuing, frontal → parietal

Attentional reorienting activates a central frontoparietal system

● when validly cued (i.e., target stimulus appears in the location the cue pointed towards), stimulus was detected faster/better and showed greater activity in visual cortex ● when invalidly cued, more activity in right temporoparietal junction (TPJ) ○ hypothesis: right TPJ is involved in shifting and reorienting attention Don't forget about the age old question of It creates a sense of community that may be vital to the success of the movement. what is it?

Visual Search

● visual search: looking for something specific in a complex scene Don't forget about the age old question of Who is the vice president under lincoln for about a month?

Behavioral studies

● experiments ask subjects to find a “target” in the middle of many other “distractors” ● pop­out stimuli: easily detected stimuli with a single featural difference ● amount of distractors does not influence time taken to find target

○ suggests that detecting pop­out stimuli involves taking in scene as a whole rather than shifting/reorienting attention

● conjunction target: target stimulus has two features in common with surrounding distractors → more distractors = longer time to find target

Theoretical models

Model 1:

● to find conjunction targets, attention is directed serially to each item to find the correct target, so reaction time increases Don't forget about the age old question of What is the difference between society and culture?

● feature integration theory: perceptual system is organized in sets of feature maps ○ vision: maps represent features like color, form, texture, etc.

○ each map provides info about the location of stimuli of a specific feature ○ processing feature maps is done early and in parallel

● binding problem: how perceptual features are bound together to create a coherent representation of an object

○ proposed that focused attention is needed for this

○ subjects tend to report illusory conjunctions (ex: reporting seeing a red O in a field of red objects and lots of O’s) when task is briefly displayed → supports theory that it takes focused attention to bind features of objects together in order to find the conjunction target

Model 2:

● guided search: two things determine allocation of attention

○ activation map driven by stimulus factors

○ activation map driven by higher­level factors/behavioral goals

● visual inputs filtered and activates items in stimulus­factor map, then activates items in higher­level map that compares the features of target to prior knowledge → combining maps helps guides search

Neural processes underlying visual search

● frontal and parietal lobes also activated in visual search

● N2pc wave: negative wave in occipital and parietal regions that is related to shifting and focusing attention during visual search

Attentional Control as a System of Interacting Brain Areas

● Mesulam model: proposed a brain network including frontal, parietal, and limbic components

○ frontal: convert strategies for shifting attention to specific motor acts ○ parietal: provide frames of reference, representation of salient events ○ limbic: compute motivational relevance of tasks/events

● Corbetta and Shulman model: control of attention divided into two main systems: ○ intraparietal cortex and superior frontal cortex: prepares and applies endogenous attention to select relevant stimuli

○ TPJ and central frontal cortex: detect behaviorally relevant/unexpected stimuli in exogenous attention

Interactions between Components of the Attentional System

● default mode network: areas that become more active when someone is not giving attention to a cognitive task

Attention, Levels of Arousal, and Consciousness

Sleep and wakefulness

● reticular activating system: central region of brainstem, regulates arousal ○ most important: cholinergic nuclei of pons­midbrain junction, locus coeruleus nuclei, and raphe nuclei 

○ cholinergic nuclei: acetylcholine

○ locus coeruleus: norepinephrine

○ raphe nuclei: serotonin

○ moderate degree of consciousness, controlled by circadian clocks

● stages of sleep:

Consciousness

1. physiological meaning: wakefulness

2. abstract meaning: subjective awareness of the world

3. self­awareness

Neural correlates of consciousness in normal subjects

● studies of brain activity while stimulus shifts in and out of focus

● binocular rivalry: when left and right eyes are shown different stimuli and perception switches back and forth between the two stimuli

○ ex: showing a house to one eye, and a face to another eye → fMRI studies show that fusiform gyrus activates when consciously perceiving the face, but

hippocampal activation when perceiving the house

● activity in visual association cortices are necessary for visual awareness, but not sufficient

Neural correlates of consciousness in pathological conditions

● blindsight: damage to primary visual cortex, blind in corresponding contralateral visual field

○ stimulus presented in blind spot (scotoma) is not seen, but when forced to respond to stimuli in blind spot subjects report correctly (more than just chance) while saying they have seen nothing

○ the unseen stimuli elicit activity in extrastriate regions of primary visual cortex → supports conclusion that visual association areas are necessary for awareness, but not sufficient

Emily Wu

emilyw12@stanford.edu

Chapter 13: Executive Functions

● executive functions: supervise/regulate other cognitive functions

● mostly elicited by prefrontal cortex

● Environmental Dependency Syndrome: patients with damage to anterior+medial parts of frontal lobe acted according to their environment, not their own goals

○ imitation behavior: patients mimicked whatever the interviewer did

○ utilization behavior: immediate environmental stimuli trigger behavior

■ ex: seeing a flight of stairs and walking upstairs even if you didn’t want to Prefrontal Cortex and Executive Function

● executive function has two roles:

○ creating rules for behavior

○ controlling rules to use in the proper context

● bilateral prefrontal damage in monkeys results in deficits in cognitive functions, but unilateral damage didn’t

● prefrontal cortex, posterior parietal cortex, anterior cingulate cortex, basal ganglia all important in executive function

● increased intelligence is associated with increased prefrontal cortex size, not overall brain size → humans and great primates have a disproportionately large prefrontal cortex compared to overall brain size

Organization and connectivity of the prefrontal cortex

● lateral prefrontal cortex: on the outer side of the

cortex, split into two parts

○ dorsolateral prefrontal cortex (top)

○ ventrolateral prefrontal cortex (bottom)

● orbitofrontal cortex: ventral (bottom) surface of

frontal lobes

● ventromedial cortex: along the middle, divided

into two parts

○ dorsomedial prefrontal cortex (towards

the bottom and back) includes anterior cingulate

gyrus­­most important for executive function

○ frontopolar cortex: anterior parts (front) of

prefrontal cortex

● prefrontal cortex → connections

○ bidirectional connectivity with thalamus

○ direct connectivity with secondary sensory cortices

○ direct link to posterior parietal cortex

○ projections from hippocampus

○ bidirectional connection with amygdala

Consequences of damage to the prefrontal cortex

● prefrontal damage can lead to two syndromes:

○ dysexecutive syndrome: damage to lateral prefrontal cortex; no deficits in intelligence, but cannot plan, complete projects, or have insight to actions; will confabulate­­deny that they have a problem and create implausible explanations

○ disinhibition syndrome: damage to ventral and medial prefrontal lobe; normal cognitive functions, but cannot inhibit their own actions (i.e., prevent self from doing socially unacceptable things)

● Phineas Gage​: damaged orbitofrontal lobe and medial prefrontal lobe in an accident, had disinhibition syndrome

● all prefrontal damage incidents: problems with forming,updating, and implementing rules for effective/appropriate behavior

Establishing and Modifying Behavioral Rules

Initiating rules for behavior

● damage to lateral prefrontal cortex: difficulty making mental plans and motor movements, don’t respond as much to world around them, withdrawal from society and little interest in things

● single­unit recordings show that neurons in prefrontal cortex carry info about different rules, more neuron activity=more rule relevance to context

Inhibiting rules for behavior

● suppression of unimportant/distracting info or behaviors

● lateral prefrontal cortex important for inhibition

● ADHD: difficulty inhibiting behavior even after a signal says to stop

Shifting among rules for behavior

● Wisconsin Card Sorting Test: used to test rule shifting; each card has 1­4 shapes of different colors → subjects asked to sort cards based on number, color, or shape → rule changes after certain number of cards

● perseveration: patients with prefrontal damage continue to sort cards with a previous rule despite knowing that it’s wrong

Hierarchical models for executive function

● topography of prefrontal cortex: posterior regions = simple rule processing, anterior regions = complex, abstract processing

Control: Matching Behavior to Context

Conflict monitoring

● conflict monitoring: knowing when an event requires additional resources to process ○ increased activity in anterior cingulate gyrus in high­conflict processing ○ Stroop task: reading color names in the text of a different color → increased activity in anterior cingulate gyrus when color and text don’t match

● error­related negativity (ERN): a negative electrical potential taken from scalp readings from EEG; happens in two instances:

○ when subject does something they realize is incorrect (response ERN) ○ to give feedback to subject that an action didn’t produce desired result (feedback ERN)

Working Memory: Maintaining Information and Rules over Time

● working memory: temporary maintenance/manipulation of information ○ an active process that also keeps out irrelevant information

● delay­period activity: delay period=time between initial activation of information and the use of the information to do something

○ neurons in dorsolateral prefrontal cortex fire continuously in delay period

Activity in lateral prefrontal cortex:

● typically lasts entire length of delay period

● increases as more information is held in working memory

● increased activity is associated with better working memory

● increased activity is associated with resistance to distractions

● tends to be greater when information needs to be manipulated in working memory rather than simply being held there

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