Week 7: cerebral cortex organization models

4 theories of cortex organizaiton

connectionism, cellular connection, cortical lateralization or asymmetry of function, cognitive stages of motor processing

connectionims theory

based on neuroanatomy, bundles of axons connect the various brain areas together.

Commissural fibers of connectionism theroy

myelinated and unmyelinated axons that cross midline and interconnect hemispheres

example of commissural fibers

corpus callosum, interconnects frontal, parietal, temporal, occipital lobes

Association fibers of connectionism theory

myelinated and unmyelinated axons that interconnect areas of the same cerebral hemisphere

example of associated fibers

arcuate fasciculus-connects temporal, parietal, frontal lobes on same hemisphere

-responsible for Wernicke-Geshwind model of language

projection fibers of connectionism theory

myelinated and unmyelinated axons project up and down the neuroaxis (cranial and caudal

example of projection fibers

internal capsule

Cellular connectionism theory

combo of localization and connectionism theories

the cellular connectionism theory states all hemispheric functions are dependent on...

discrete identifiable collections of cells (brodmann areas) that act through integration, specific connections wiht other related cell groups both within the hemispheres, across hemispheres and in other parts of brain and spinal cord

2 things for evidence of cellular connectionism theory

wernike-Geshwind model of language and 5 cortical areas involved in motor control

wernike-geschwind model of language

multiple areas and their interconnections are responsible for whole function of speech

what areas are involved in the werkine-geschwind model

vision, auditory, tactile/proprioception, left wernickes area, left angular gyrus, left artucate fasciculus, left pre/post central gyri, left brocas area

visual input

primary visual (17) and association visual cortex (18,19)

auditory input

primary auditory cortex (41,42)

left wernickes area

area 22, turns auditory input into meaninful units or words (receptive aphasia)

-turns it to semantic code

left angular gyrus

39 (parietal), combines sensory, visual, auditory input into patterns of letters, words, or possibly sensory feelings

left arcuate fasciculus

joins posterior brain (receptive area) to anterior brain (expressive area)

Left pre and post central gyri

sensory (3,1,2) and motor areas (4)

-uses face, jaw, lips, pharynx, larynx, tongue, diaphragm

-directs muscle activity adn provides on-going feedback of speed movements and produces and monitors speech patterns

left broacs area

formulation of words, sentences, expressions (expressive aphasia)

If the brain gets damage to the following areas, what issue do they have

1)wernickes area

2)arcuate fasciculus

3)facial areas

4)brocas area

1) receptive aphasia

2)conduction aphasia

3)dysarthria

4)expressive aphasia

the 5 cortical areas involved in motor control produce

visually oriented, goal oriented, and voluntary movement

5 areas fo motor control

MI, SI, PMA, SMA, posterior parietal lobe

M1 is the origin of

majority of CST (anterior and lateral)

M1 arrangement

somatotopically

M1 affects which side

contralateral side

when is M1 active

both immediately before and during movement

-last one to fire prior to movement onset

microstimulation of M1 contracts

individual muscles

M1 discharge frequency effects

encodes amount of force and rate of force production to move the limb, does not correspond to position changes of limb

M1 test with monkey was done by

Evarts

3 conditions for MI test with monkeys/flexion

A: wrist flexion with no load (flexors active, no extensors)

B: wrist flexion with flexion load (very active flexors no extensors)

C: wrist flexion with extension load (no flexors, extensors very active)

MI direction monkey test was done by

Georgopoulos

individual MI neurons are sensitive to

movement direction when monkeys move during a center-out task (targets in circle), fire predominantly to movements in prefered direction but also to a lesser degree in other directions

MI population vectors

vectorial summation of single-cell contributions produce population vector that can predict movement in space.

-reaching out command

-length and direction represent firing intensity over a certain period

sensory cortex( si) in motor control

information flows between (back and forth) between MI and Si

-area 4

PMA is what broadmann area

6

PMA

-activity can proceed MI by up to 1 second

-planning and production of complex, purposeful movements

-visually and sensory guided movement

-involved in proximal and axial muscle control

SMA is which brodmann area

6 (medial)

SMA

complex movements and sequencing, active during imagined, complex movements, role in bimanual movements (2 things at once)

Posterior parietal lobe is what brodmanns areas

5,7

posterior parietal lobe

visually guided movements, responsible for spatial relationships, sensorimotor transformation

2 pathways coming from occipital lobe (as part of posterior parietal area function)

dorsal pathway to parietal lobe, and ventral pathway to anterior/inferior temporal lobe

Dorsal pathway functions

where are objects in space? how are objects oriented to eachother?

ventral pathway functions

physical qualities, size, shape, weight,etc

cortical lateralization or asymmetry of function theory

division of labor between hemispheres

-each processes same information just differently and for different content

right hemisphere

holistic logic

-spatial organization of sensory, music (tone), drawing, symbolic language (facial gestures, tone rhythm, body language)

left hemisphere

sequential logic

-use syntactic rules for communication and math, sequences, math, spoken/written words, verbal language

Braid development theory by Kolb and Whishaw

both hemispheres appear to be functionally specialized at birth, both appear plastic and capable assuming some function of other hemisphere

Equipotentiality theory

either hemisphere has equal potential for developing a certain function

parallel-development theory

both hemispheres are destined to specialize a certain function

Brain development theory by Moscovitch

possibly that one hemisphere actually inhibits the other hemisphere

-other wont have same functions

-space and function

-develops inhibition at 5-8

From stimulus to movement initation is the

reaction time

from movement initiation to movement termination

movement time

how many stages of cognitive processing

seven stages in order to produce motor behavior

When do these 7 stages occur

during reaction time period

-Serial processing model (in order)

Order

detect, identify, memory search, decision, response selection, response organization, response execution

Detect-visual

store visual info

Capacity:17 words

Code: physical

Decay:200 msec

Detect-auditory

store visual info

capacity: 5

physical:physical

decay:1500 msec

Identify-working memory

Capacity: chunk (3 chunks if pure memory, 7 chunks if LTM)

Code:semantic, symbolic

Decay: 7 seconds

detect+identity =

encode

Memory search (LTM)

chooses to store info into LTM and places info into chunks, of they choose not to store into LTM, it can be skipped

Memory search specifics

capacity: infinate

code:semantic

decay:infinite

decision

decide whether or not to act, if timing is appropriate, motivation or desire to act

(TBI may have issues with this)

Response selection

choose from a number of motor responses

HICKS LAW

explain hicks law

-very quick reaction time if 1 target

-long reaction time if many targets

Response organization

organize motor output as movement distance, direction, speed

-Use PMA, BG, cortex, MI

response execution

execute motor output as to muscles, force, rates of force

-MI