Ch 13 - Regulating Brain States

covert spatial attention

a form of visual spatial attention that can be shifted from one location to another w/o movement of the eyes, head, etc

• mental shift of attention; “secretive”

• Helmholtz → improves perception

involuntary attention

a form of attention in which external stimuli “grab” a person’s attention against their will or w/o them having conscious control

• AKA bottom-up / stimulus-driven/ exogenous attention

salient

grabbing/deserving attention

voluntary attention

attention that can be directed at will; intentional shift/focus

• ex: when you are looking for specific item in cluttered scene / listening for specific sound within other sounds

serial search

intentional roving of attentional spotlight

parallel search

salient stimuli automatically pop out

saliency map (model of attention)

the idea of a map-like neural representation of external space in which each neuron’s firing rate correlates w/ the salience of the stimuli at the encoded location

• all parts of scene analyzed in parallel to identify features; info then combined into single ______

  • this specifies all attention-deserving locations

    • competitive algorithm determines most salient location (attention drawn here)

inhibition of return

tendency of visual spatial attention (both covert and overt) to not return to locations on which it had just been focused

• decreases salience of winning location

  • prevents attention from getting stuck at most salient location

superior colliculus

major midbrain region that receives visual & auditory info; projects to pulvinar and brainstem saccade generators

• called optic tectum in non-mammalian vertebrates

  • critical in neural circuits underlying attention

• stimulation can guide covert and overt spatial attention

pulvinar nucleus

a thalamic nucleus that receives visual inputs from superior colliculus and projects to variety of extrastriate cortices (most visual cortices)

• involved in control of visual spatial attention

  • conveys attention-related signals to visual cortices

cued spatial attention task

behavioral task in which subject is given a signal (a cue) indicating where they should direct their spatial attention

• key finding → monkeys react more quickly when stimuli appear at attended location

  • covert voluntary attention strengthens response to neuron’s preferred stimuli

frontal eye fields (FEF)

play role in control of voluntary eye and head movements

• activity correlates w/ controlling covert voluntary attention

hemispatial neglect

a clinical condition in which subject has trouble paying attention to stimuli on left side of external world (usually in body-centered or world-centered coordinate frames)

• typically caused by lesion on right side of brain

behavioral arousal

a condition in which all sorts of stimuli become more likely to elicit a response, b/c organism has experienced a threatening stimulus

• state of “heightened attention”; caused by highly salient stimuli

electroencephalogram (EEG)

recordings of cortical activity made thru relatively large electrodes (most often on scalp), each of which averages electrical activity of thousands of neurons (rather than single neurons)

• waves generated by cortical neurons and changes in them reflect changes in behavioral state

EEG desynchronization

a decrease in amplitude (wave height) and increase in frequency of EEG

• typically associated w/ behavioral arousal (and REM sleep)

  • caused by synchronous firing of neurons

ascending arousal system

set of neural pathways that, when stimulated electrically, can elicit EEG desynchronization

• includes axons of locus coeruleus and peribrachial neurons

  • 2 principal systems

    • cholinergic neurons

    • locus coeruleus

locus coeruleus

small group of neurons near the fourth ventricle; use norepinephrine as main neurotransmitter; project throughout most of the brain

• involved in regulating behavioral arousal → functions as brain arousal system

tyrosine hydroxylase

enzyme that is needed for synthesis of dopamine, norepinephrine, and epinephrine b/c it converts L-tyrosine into L-dopa (immediate precursor of dopamine)

• used to see noradrenergic projections of locus coeruleus

dopamine beta-hydroxylase

enzyme that converts dopamine to norepinephrine

• used to see noradrenergic projections of locus coeruleus

epinephrine

hormone (chemically related to norepinephrine) secreted from adrenal gland and involved in stress response

• AKA adrenaline

  • locus coeruleus neurons increase firing rate as levels of this hormone in blood rise

NOT ON EXAM

signal-to-noise ratio

ratio between amplitude of signal and noise in which that signal is embedded

• higher the ratio, the “cleaner” the signal

  • locus coeruleus activation increases ___ of neocortex

NOT ON EXAM

adrenergic receptors

family of G protein-coupled receptors that bind norepinephrine as well as epinephrine (adrenaline)

• commonly divided into alpha- and beta-adrenergic receptors

NOT ON EXAM

rapid eye movement (REM) sleep

phase of sleep in which subjects tend to exhibit jerky eye movements and desynchronized EEG

• subjects that suddenly wake from REM sleep often report vivid dreams

EEG rhythms/waves

• beta and gamma = fast, low-amplitude oscillations

• alpha = 8-13 Hz

• theta = slightly slower (4-8 Hz)

• delta = even slower (1-4 Hz)

• ALSO…

  • very slow (<1 Hz)

  • very fast (12-14 Hz) = sleep spindles

sleep stages

• light sleep (stage 1)

• intermediate stages

• deep sleep (stage 4) → delta waves

  • return to stage 1 or REM

• REM (stage 5) → desynchronized EEG

thalamic reticular nucleus

a thalamic cell group that inhibits neurons in dorsal thalamus and receives input from both dorsal thalamus and neocortex

• alternating pattern of activity between thalamic reticular neurons and thalamocortical neurons

  • involved in generating rhythmic patterns of thalamocortical activity (during slow-wave sleep)

postinhibitory rebound

tendency of some neurons to fire burst of action potentials after they have been “freed” from inhibition (disinhibited)

• displayed by disinhibited thalamocortical neurons (in dorsal thalamus)

rhythmic oscillations

neurons in dorsal thalamus have role in generating slow rhythms of cortical EEG

• looping connections can generate rhythmic oscillations (loops between corticothalamic and thalamic reticular neurons)

  • thalamic reticular nucleus (inhibitory projections) → dorsal thalamus / thalamocortical neurons (excitatory projections) → neocortex (excitatory projections) AND back to thalamic reticular nucleus → dorsal thalamus and thalamic reticular nucleus