bio psych - chpt 14

dyslexia

impairment in learning to read/write; most common learning disability

varies with language orthography: deep, shallow

all orthographies have slow word recognition

variations in behavioral manifestations across lagnauges - different cognitive dysfunctions associated with different forms

role of extended cortical networks and cortical connectivity

reduced sensitivity in the left temporoparietal, occipital, and inferior frontal cortex

reduced gray matter volume in the left superior temporal sulcus and right superior temporal gyrus across orthographies

right and left temporal abnormalities

reduced functional connectivity between medial geniculate nucleus and auditory cortex

training programs for dyslexia

devised to stimulate plasticity in the reading-related brain systems

music training, neuroplasticity-based auditory training, computer-modified speech, assistive learning devices

brain is plastic

experiences that change the brain

development, culture, preferences, coping

learning is common to these experiences

nervous system has potential for physical or chemical change, enhances its adaptability

learning

change in an organisms behavior as a result of experience

memory

ability to recall or recognize previous experience

engram (memory trace)

a mental representation of a previous experience

corresponds to a physical change in the brain, most likely involving synapses

Pavlovian conditioning

learning procedure whereby neural stimulus such as tone (CS) comes to elicit a response (CR) because of its repeated pairing with some event such as the delivery of food (UCS): also called classical conditioning of respondent conditioning

conditioned stimulus

originally neutral stimulus that triggers a conditioned response (CR) after association with an unconditoned stimulus

unconditioned stimulus

stimulus that unconditionally —naturally and automatically— triggers an unconditioned response

unconditioned response

unlearned, naturally occuring response to the unconditioned stimulus, salivation when food is in mouth

conditioned response

learned response to a formerly neutral conditionedfr stimulus

fear conditioning

unpleasant but harmless stimulus used to elicit an emotipnal response : fear

eyeblink conditioning

a tone (CS) associated with a painless puff of air (USC) to participant’s eye

blinking is normal reaction (UCR) to puff of air

learning occurs when blinking is response to the CS alone (CR)

operant conditioning (instrumental conditioning)

consequences (obtaining a reward) of particular behavior (pressing a bar) increase or decrease probability of behavior occurring again

operant learning not localized to any particular brain circuit

• necessary circuits vary with task requirements

Thorndike’s puzzle box

cat gradually learned that its actions had consequences

cat touched releasing mechanism only by chance on initial trial as it paced restlessly inside box

cat learned that something it had done opened the door, tended to repeat its behaviors from just before door opened

implicit memory

unconscious memory - subjects demonstrate knowledge, such as a skill, conditioned response, or recalling events on prompting, cannot explicitly retrieve information

explicit memory

conscious memory - subjects can retrieve item and indicate that they know they retrieved correct item

priming

using stimulus to sensitize nervous system to later presentation of the same or similar stimulus; unconscious learning

often used to measure implicit memory

Gollin failure test

retention test, partipants identify image sooner, indicating some form of memory for the image

amnesic subjects show improvement on this test, even though they do not recall having taken it

Pursuit-rotor task

people with amnesia, partial or total loss of memory, perform implicit memory tests at normal

presented with same task a week later, both controls and amnesics take less time to perform

amnesics fail to recall having performed the task before

declarative memory

ability to recount what one knows, to detail time, place, and circumstances of events; often lost in amnesia

procedural memory

ability to recall a movement sequence or how to perform some act or behavior

learning set

rules of the game; implicit understanding of how a problem can be solved with a rule that can be applied in many different situations

differentiating two memory categories

commonly used dichotomies

one memory category necessitates recalling specific information

the other refers to knowledge of which we are not consciously aware

encoding and processing memories

brain processes explicit and implicit information differently

implicit information is processed in a bottom-up or data-driven manner

• information is encoded in the same way it was perceived

explicit information is processed in a top-down or conceptually driven manner

• subject reorganizes the information before it is encoded

task roles

implicit tasks - person has passive role

explicit tasks - person has active role

storing memories

information from different sensory modalities (vision, audition) is processed and stored in other neural areas

Jeffrey Binder and colleagues

performed meta-analysis of 120 fMRI semantic memory studies

found a distinct network compromising seven different left-hemisphere regions, including regions of parietal lobe, temporal lobe, prefrontal cortex, and posterior cingulate cortex

not all regions are active at once when semantic memory is stored

subregions relatively specialized for specialized for specific object characteristics or types of knowledge

extensive network similar to default network that is active when participants are resting rather than engaged in specific cognitiive tasks

semantic processing constitutes large component of cognitive activity during passive states

autobiographical memory

episodic memory for events pegged to specific place and time contexts

how and where autobiographical memories are stored

key regions - ventromedial prefrontal cortex (vmPFC) and hippocampus, pathways between them

• discriminability in the hippocampus: similar for old and new memories

• discriminability in prefrontal cortex: much poorer for new memories

change in the engram in prefrontal cortex over two years, hippocampus remained stable

loss of personal memory

KC suffered TBI produced cortical lesions

• cognitive abilites and STM intact

• episodic autobiographical amensia covering entire life from birth damaged

hippocampal injury also associated with poor episodic memory

• reduced hippocampal activity occured during episodic memory

• retrieval associated with impaired episodic memory

• increased cmPFC activity during memory retrieval found as result pf parietal compensation for hippcampal dysfunction

highly superior autobiographical memory

people display virtually complete recall for events in their lives, usually beginning around age 10

many can describe any episode, including day of week and date

individuals with HSAM

• areas likely as other participants to develop false memories

• show superior personal memories but not superior cognitive functioning

HSAM appears to require an experience that is part of the individual’s personal narrative

dissociating memory circuits

Karl Lashley searched unsuccessfully for neural circuits underlying memories

• severity of memory disturbance related to size, not location, of injurt

WIlliam Scoville

performed bilateral medial temporal lobe resection on young man (H.M).

seizures originated in region of amygdala, hippocampal formation, and associated subcortical structures, Scoville removed them bilaterally

disrupting explicit memory

after surgery, H.M. had severe amnesia, lacking explciit memory -coudl not recall anything that happened after the surgery

H.M. had above average IQ, performed well on perceptual tests could recall events from childhood

H.M’s performance on implicit memroy tests was left intact

disrupting implicit memory

patient J.K.

impaired implict memory with intact explicit memory

• developed Parkinson’s in his mid 70s started to have memory problems at 78

  • damage to basal ganglia

• impaired ability to perform tasks that he had done all his life

  • turning off radio

• could still recall explicit events

Patient Boswell’s Amnesia

boswell developed herpes simplex encephalitis

• recovery from acute symptoms

• low average intelligence from neuro infection

• severe amnesic syndrome

amnesia and brain pathology documented -critical samage of bilateral destruction of temporal media regions

loss of basal forebrain and posterior part of orbitofrontal cortex and insular cortex from lateral fissure

primary structures for explicit memory

medial temporal region

• hippocampus

• amygdala

• entorhinal cortex

• parahippocampal cortex

• visuospatial memory

prefrontal cortex

other closely related structures

parahippocampal cortex

receives connections from parietal cortex

believed to take part in visuospatial processing

perihinal cortex

receives connections from visual regions of ventral stream

believed to take part in visual object memory

entorhinal cortex

receives projections from parahippocampal and perirphinal cortices

integrative function: first area to show cell death in alzheimers

visuospatial memory

visual information to identify object’s location in space

lab animals and human patients with selective hippocampal injury have severe deficits in various forms of spatial memory

monkeys with hippocampal lesions have diffiuclty learning location of objects

hippocampus and spatial memory

animals (humans included) with especially good spatial memory should have difficulty learning locations of objects

• monkeys with hippocampal lesions have difficulty learning locations of objects

  • visual-recognition task: object-position task

• hippocampal formation in food-storing birds and rodents is larger than that of birds who are not food cachers, and rodents that do not store food

spatial cells in hippocampal formation

three classes of spatial cells in rat and mouse hippocampus medial and entorhinal cortex

• place cells -discharge when rats are in spatial location, regardless of orientation

• head direction cells -discharge whenever rat’s head points in particular direction

• grid cells discharge at many locations, forming virtual grid invariant to changes in rat’s direction, movement or speed

place cells and head cells -location

found in hippocampus and closely related structures

grid cells -location

found in entorhineal cortex, major afferent route into hippocampus

reciprocal connections for explicit memory

neocortex projects to entorhinal cortex, projects back to neocortex

• signals from medial temporal regions to cortical sensory regions jeep sensory experience alive in brain: neural record outlasts experience

• pathway back to neocortex means it is kept apprised of information processed in medial temporal regions

frontal lobe’s role in explicit memory is subtler than that of medial temporal lobe

frontal lobe and STM

frontal lobe participates in many forms of STM

all sensory systems project to frontal lobes

• during tasks in which monkeys must keep information in STM over a delay, certain cells in frontal cortex will fire throughout delay

  • animals that have not learned task show No such cell activity

Korsakoff syndrome

tracing explicit memory circuit

• permanent loss of the ability to learn new info (anterograde amnesia) and retrieve old info (retrograde amnesia)

• caused by diencephalic damage from chronic alcoholism or malnutrition that produces vitamin B1 deficiency

• memory disturbance probably severe because damage includes forebrain and brainstem structures

Mortimer Mishkin and colleagues

neural circuit for explicit memory incorporates evidence from both humans and lab animals with injuries to temporal and frontal lobes

• temporal lobe structures

• frontal lobe structures

• medial thalamus

• basal forebrain- activating systems

proposed circuit for implicit memory

• basal ganglia

• ventral thalamus

• substantia nigra

• premotor cortex

reciprocal neural circuit proposed for explicit memory

sensory and motor neocortical areas connect to medial temporal regions

basal forebrain structures play role in maintainining appropriate activity levels in other forebrain structures to process information

temporal lobe hypothesized to be central to long term explicit memory formation

prefrontal cortex central to maintaining temporary (ST) explicit memories and memory for recency (chronological order) of explicit events

consolidation of explicit memories

hippocampus consolidates new memories

in consolidation, or stabilizing a memory trace after learning, memories move from hippocampus to diffuse regions in neocortex

once memories move, hippocampal involvement is No longer needed

when memory is replayed in mind, its open to further consolidation

new info constantly being integrated into existing memory networks

possible to erase negative memories using amnesic agents when memory is revisted

neural circuit for implicit memories

basal ganglia recieves imput from entire neocortex and sends projections first to ventral thalamus and then to premotor cortex

• basal ganglia also receive widely and densely distributed projections from dopamine-producing cells in substantia nigra

  • dopamine appears necessary for basal ganglia circuits to function and may indirectly participate in implicit memory formation

unconscious nature of implicit memory

Mishkin believes that implicit memories are unconscious because connections between basal ganglia and cortex are unidirectional

• basal ganglia receive information from cortex but do not project back to cortex

• for memories to be conscious, must be feedback to the cortex

  • medial temporal lobe projects back to cortex, explicit memories are conscious,

emotional memory

memory for affective properties of stimuli or events

can be implicit or explicit

amygdala is critical

• damage to amygdala abolishes emotional memory but has little effect on implicit or explicit memory

amygdala - neural circuit for emotional memories

close connections with medial temporal cortical structures and rest of cortex

sends projections to

• brainstem structures that control autonomic responses -blood pressure and heart rate

• hypothalamus, controls hormonal systems

• periaqueductal gray matter (PAG), affects pain perception

• basal ganglia top tap into implicit memory system

structural basis of brain plasticity

neural level, memory associated with changes at synapse

• synapse -one neuron influences another neuron

finding neural correlates of memory:

• determine how synaptic changes are correlated with memory in mammalian brain

• localize synaptic changes to specific neural pathways

• analyze nature of synaptic changes themselves

Eric Kandel and collegues (2015)

measured neurotransmitter output from sensory neuron

verified that less neurotransmitter is released from habituated neuron than nonhabituated one

sensitization response

enhanced response to some stimulus; occurs within particular context

• organism becomes stimulus hyper responsive to stimulus

neural circuits participating in sensitization differ from those participating in habituation response

opposite of habituation at molecular and behavioral levels

associative learning

entails enduring neural change in postsynaptic cell after EPSP from presynaptic cell crosses synaptic gap

long term potentiation (LTP)

involves persistent strengthening of synapse based on recent activity patterns, produces long-lasting increase in singal transmission between two neurons

in response to stimulation at synapse. charged amplitude of excitatory postsynaptic potential lasts for hours to days or longer

discovery of LTP led to revolution in thinking about how memories are stored

long term depression (LTD)

low-frequency stimulation produced decrease in EPSP size

if LTP is mechanism for creating memories, LTD is mechanism for clearing out old memories

LTP/LTD basis for understanding synaptic changes underlying memory

enhanced LTP in recruited pathways is seen when animals learn to solve problems

LTP produces enduring changes in synaptic changes in synaptic morphology resembling those seen in memory g

glutamate action

acts on two types of receptors on post-synaptic membrane

• APMA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)

  • normally responds to glutamate

• NMDA (N-methyl-D-aspartate)

  • doubly gated channels

  • normally blocked by magnesium (Mg2+) ions

LTP/LTD

two events must occur together or rapidly for NMDA receptors to open

• depolarization of postsynaptic membrane, displaces Mg2_ from pore (strong electrical stimulus)

• activation by glutamate from presynaptic neuron (weak electrical stimulation)

• strong and weak stimuli have been paired

GABA interneurons

experiments on inhibitory GABA interneurons demonstrate phenomena similar to LTP and LTD: iLTP and iLTFD

• i -inhibotory

generally believed that inhibitory neurons were not plastic, they are

• plasticity of GABAergic (inhibitory) synapses plays fundamental roles in modulating networks of excitatory neurons

measuring synaptic change

experience could change brain -modifying existing circuitry or creating novel circuitry

actuality -plastic brain uses both strategies

modifying existing circuits

neurons change their structure in response to changing experiences

changes in number of dendrites can be used to infer synaptic changes

• more dendrites provide more connections

new synapses can form between already connected neurons or between neurons that were not previously connected

physical basis of memory

relative to neural control connection, number of synapses between Aplysia’s sensory neuron and motor neuron decline as result of habitation, and increases as result of sensitization

structural changes may underlie eduring memories

enriched experience and plasticity

raising cats in enriched enclosures is associated with

• enhanced later learning

• increased brain weight

• changed dendrite length

• changed glial, vascular and metabolic processes

• more synapses per neuron

• more astrocytes, blood capillaries

• higher mitochondrial volumes

Fem—Lei and William Greenough (1982)

placed patches over one eye of each rat so contralateral hemisphere was deprived of visual input; trained rats on maze

conclusion: visual cortex of trained hemisphere (received input from eye without patch) had more extensive dendrites

Randy Nudo and colleagues (1997)

mapped motor cortex of monkeys; noted striking individual differences in topography

conclusion: learning new motor skills, rather than repetitive motor use, shapes functional topography of motor cortex

Jon Jaas (2000)

showed that when sensory nerves in one limb are severed in monkeys; relevent part of cortex No longer responds to limb stimulation

deafferented cortex begins to respond to input from other body parts

creating novel circuits

more recently, imaging techniques such as transcranial magnetic stimulation (TMS) and fMRI

Ramachandran (1993)

indirectly measured cortical maps in individuals with limb amputations

when face was stroked softly with cotton saw, amputees reported sensations of being touched in amputated hand

may explain phantom limb pain

cortical reorganization

when a hand amputee’s face is stroked lightly with cotton swap (a) person exepriences stroke as light touch on missing hand (b) touch to the face too

deafferented cortex forms representation of amputated hand on face

as normal somatosensory homunculus, thumb is disproportionately large. information form

Arnold Scheibel and colleagues (1993)

relationship between dendrite size in Werncike’s area

• level of education increases neuron complexity

• more extensive dendritic branching found in females

• large differences in trunk and finger neurons appeared in brains of people with high level of finger dexterity maintained over long periods

general conclusion

• specific experiences can produce localized changes in synaptic organizatione of brain, such changes form structural basis of memory

experience and neuronal complexity

confirmation of Scheibel’s hypothesis that cell complexity is related to computational demands required of cell

neurons representing body’s trunk area have relatively less computational demands than cells representing finger region

cells engaged in higher cognitive functions (languge -wernicke’s area) have greater computational demands than those engaged in finger functions

epigenetics of memory

specific sites in DNA of neurons involved in specific memories might exist in either methylated or nonmethylated state

• fear conditioning associated with rapid methylation, if methylation blocked, No memory

epigenetic mechanisms mediate synaptic plasticity broadly, learning and memory

epigenetic changes related to experiences may contribute to inheritance of phenotypes across generations

hormones and plasticity

structural differences in cortical neurons of male and female rats depend on gonadal hormones

• gonadal hormones can influence cell structure and behavior in human females across menstrual cycle (some inconsistent data; hard to maintain a long term trend)

• estrogen level drops produce increased numbers of spines on pyramidal cells throughout neocortex but decreased spine density in hippocampus

glucocorticoids

released from adrenal cortex in times of stress

assist in metabolism of proteins and carbs and control of sugar levels in blood and cells

steady levels of glucocorticoids that are seen with prolonged stress may be neurotoxic

• glucocorticoids can kill hippocampal cells

nerve growth factor

neurotrophic factor stimulates neurons to grow dendrites and synapses, in some cases, promotes survival of neurons

brain-derived neurotrophic factor

may enhance plastic changes, growth of dendrites and synapses

increased levels when animals learn to solve problems

behavioral sensitization

escalating behavioral response to repeated administration of psychomotor stimulant, amphetamine, cocaine, nic, drug induced behavioral sensitization

associated with increased receptors, synapses, dendrites

changes localized to regions that receive large dopamine projection

psychoactive drugs appear to have parallel action: lead to increased behavioral sensitivity to their actions

guiding principles of brain plasticity

behavioral change reflects brain change

all nervous systems plastic in same general way

plastic changes are age-specific

prenatal events can influence brain plasticity throughout life

plastic changes brain-region dependent

experience-dependent changes interact (metaplasticity)

plasticity has pros and cons

ways to recover from TBI

learn new ways to solve problems

reorganize brain to do more with less

generate new neurons to produce new circuits

three-legged cat solution

when a cat loses a leg, it usually can compensate by not growing a new leg but learning how ot walk with only three

same ability to compensate also present in humans

• person who loses certain ability, being ale to write with right hand, can compensate by learning to write with left

new circuit solution

brain can form new connections and do more with less in response to injury

amount of recovery is increased significantly if person also engages in some form of intervention

• behavioral therapy

  • speech or physiotherapy

• pharmacological therapy

  • nerve growth factor, amphetamine

fetal tissue implantation

limited success to date; more suitable when only small number of cells needed

• dopamine-producing cells in substantia nigra for Parkinson disease patients

epidermal growth factor

to replace lost cells

neurotrophic factor stimulates sub ventricular zone, generates cells that migrate into striatum, differentiate into neurons and glia

trophic factors may be useful treating brain injury in the future