Neural Bases - Somatosensory & Associational Pathways

Front 1

Association pathways -- name some of them

Back 1

- superior longitudinal fasciculus (includes arcuate fasciculus -- language areas)

- inferior longitudinal fasciculus

- cingulum

- superior occipitofrontal fasciculus

- uncinate fasciculus

- arcuate fibers (U-shaped)

- callosal radiations

Front 2

Split Brain - history

Back 2

- first subject 1961; used to treat epilepsy; initially clipped entire CC and anterior commisure (newer procedure spares splenium/posterior of CC)

After surgery, people appeared "normal" -- walk, read, talk, play sports, etc

Front 3

Experiments with split brain subjects

Back 3

-Words (objects) flashed to R field of vision could be read aloud, written and selected with R hand, but not left

- flashed to L field could not be read aloud or written, but could be selected with L hand -- not the R

--> language on L side, which is where R field of vision is processed. if flashed to R field, have language for it. if flashed to L field, processed by R field, and no language for it.

Front 4

split brain subjects -- chimeric figure

Back 4

woman on L vis field; man on R

- asked to choose face seen with L hand --> picks woman (L vis field processed by R hemi, which controls L hand)
- asked to NAME face seen --> says man (responding to R vis field stim - lang processed in L hemi)
- choosing vs. verbal will present diff responses

Front 5

Hemispheric differences

Back 5

R hemi: superior in spatial tasks

- ea hemi flashed a drawing and corresponding hand drew (L visfield flashed; L hand draw -- all R hemi processing; v/v)
- L hand (R hemi) consistently better -- even for R-handed subjects

Front 6

Cortical divisions/functions

Back 6

Motor/premotor (frontal): skeletal muscle movement;

Parietal: sensory info from skin, ms system, viscera, taste buds;

Prefrontal: coordination info from other association areas, controls some bxs, reasoning skills;

taste, smell

Temporal: hearing

Occip: vision

NONE of these areas alone controls anything in particular; control comes from interaction.

There are some primary reception areas by themselves theyonly receive the info. If impairment is in receptive area only, problem w/ receiving (e.g. blindness); but may still have visual reflexes

Front 7

How do you test recognition?

Back 7

MATCHING task. Recognition requres reception and association.

To test auditory recognition: use environ sounds, point to pic; but there is complication -- crossing modalities)

Front 8

Cortical organization

Back 8

1. Motor cortex (primary, premotor, supplementary, frontal eye fields)

2. Primary sensory cortex (auditory, visual, somatorsensory, gustatory, olfactory

3. Associational cortex (visual, auditory-visual, visual spatial...)
- any area of cortex (not sensory or motor) assoc with advanced stages of sensory info processing, multisensory integration, or sensorimotor integration.
- Cortical areas involved in higher mental fxn such as learning, remembering, thinking, speaking, perceptual judgment

Front 9

Cortical motor areas -- name them

Back 9

1. Primary Motor Cortex
2. Premotor Cortex
3. Supplemental Motor Area (wraps over longitudinal fissure)

Front 10

Primary Motor Cortex

Back 10

- lies along precentral gyrus
- activates specific groups of muscles (homunculus)
- consists of pyramidal shaped cells

Front 11

Output of Primary Motor Cortex

Back 11

- most efferents go to pyramidal tract (and 30% of CS tract comes from PrimMC)
- role is to activate specific muscle groups -- vol skilled acts

- tracts to thalamus (to activate basal ganglia -- motor control, stability, inhibition or excit, balance)

- tracts to cerebellum (via pons) -- coordination, assist timing of movements

- Opposite primary motor cortex (cross via CC -- activate for bilateral actions)

Front 12

Input for Primary Motor Cortex

Back 12

- premotor cortex
- opposite motor cortex
- somatosensory cortex (for proprioception)
- contralateral cerebellum (help time movements -- excitatory afferents. may see cerebellar problems that are because of lesions in tracts to/from cerebellum - not necessarily IN cerebellum)
- Thalamo-cortical projections (inhibitory loop from basal ganglia)

Front 13

Premotor Cortex

Back 13

- much larger than primary MC
- includes supplementary motor cortex
- essential for complex, sequential actions performed by sensory guidance
- controls proximal & trunk muscles -- need to have these stabilized in order to do anything w/ distal muscles
- active in bilateral aspects of motor patterns
- INCLUDES BROCAS AREA

Front 14

Premotor Cortex - OUTPUT

Back 14

- contributes 30% of axons in CS tract; requires more intense stimuli than primary MC to produce mvmts (more neurons needed to get actions)
- contributes to INDIRECT ACTIVATION PATHWAYS (e.g. reticulospinal) for movement preparation (postural adjustments that allow desired movements to take place)

Front 15

Premotor Cortex -- INPUT

Back 15

rostral frontal lobe fro planned movement and frontal eye fields

parietal lobe for tactile/visual-spatial information

Front 16

Supplemental Motor Area

Back 16

- activated by prefrontal planning areas for more complex motor plans
- essential for complex, sequential actions performed from memory
- lesions to SMA don't produce weakness, but rather APRAXIA
- the SMA sequences movements reuired to peform multistage tastks

Front 17

Frontal Eye Fields

Back 17

- controls voluntary saccadic eye movements (not pursuit, which is involuntary)
- R frontal eye field turns eyes to the LEFT, v/v

Front 18

Prefrontal Cortex

Back 18

- prefrontal uniquely large in humans
- connect with corresponding opposite hemi
- 2-way connections w/ associational cortex (focus visual attention, e.g.) throughout both hemis
- bilateral lesions may produce AKINETIC MUTISM (not a locked-in syndrome. also no dx significance, not localizing, just descriptive)

- working with other areas, concerned with higher brain functions: abstract thinking, decision making, anticipation, social behavior, personality, executive functions

Front 19

Frontal Lobe Syndromes

Back 19

often associate with:
- short temper
- irritability
- poor impulse control
- sociopathic personality (no associations to - what are the consequences of what i do right now)
all have to do with inability to inhibit

Examples of various syndromes:
1. Orbitofrontal syndrome -- DISINHIBITED
2. Frontal convexity syndrome -- APATHETIC
3. Medial frontal syndrome (AKINETIC)
4. Dorsolateral frontal cortex -- impaired planning, strategy, exec fxn; apathy, abulia (lack of will) personality changes -- Phinneas Gage

Front 20

Frontal Lobe Signs and Tests

Back 20

- inappropriate social bx (observe dress)

- poor decision making (history)

- akinesia/abulia (observe lack of vol mvmt, loss of will power, akinetic mutism, flat affect)

- impaired shifting of sets - (antisaccade)

-decreased generation of ideas (word fluency)

- frontal release signs (suck, root, grasp)

Front 21

Summary: Frontal Lobe

Back 21

- motor
- willful eye mvmt
- planning, executive fxns

Front 22

Parietal Lobe -- Somesthetic cortex

Back 22

Areas 3, 1, 2:
Slow adapting receptors (pain, temp)
rapid adapting cutaneous receptors (fine discrim touch)
movement receptors

Front 23

Input for Somesthetic cortex

Back 23

- Thalamic projections (somatosensory receptors)
- Callosal fibers (between hemis)
- motor cortex collaterals (e.g. sense of weight)

Front 24

Output from Somesthetic cortex

Back 24

- to motor cortex
- opposite somesthetic cortex
- posterior parietal associational cortex
- thalamus (modulate input)
- posterior gray horn of SC (incorporated into pyramidal tract) -- modulates incoming sensory info

Front 25

Somesthetic ASSOCIATION area

Back 25

- functions in stereognosis -- making sense; IDing qualities

Front 26

Angular gyrus

Back 26

- functionally part of Wernicke's Area
- Projections from visual association areas
- projections ot temporal lobe -- fxn in visual imagery

Front 27

Posterior parietal

Back 27

- receives visual associational input
- projects to frontal eye fields and pre-motor
- fxn in covert attention (right more active than left -- perception & spatial awareness)

Front 28

Inferior parietal

Back 28

- receives visual assoc and limbic input (emotion, memory)
-fxn in body schema awareness -- lesions may cause neglect or anosognosia

Front 29

Two functions of parietal association regions

Back 29

1. serves sensations and perceptions, form a single perception

2. Integrates somatosensory input, usually with visual system -- orient us to our world, spatial surroundings

R parietal predominates for these functions

e.g. old/young woman

Front 30

Left parietal function

Back 30

not as imp in spatial relations as RH, for most people

Front 31

Left parietal fxn -- Gerstmann's syndrome

Back 31

- Right-Left confusion, agraphia, acalculuia, finger agnosia
(don't memorize!!)

Front 32

Contralateral Neglect

Back 32

- damage to R parietal lobe:

- neglect part of body or space (all senses except hearing)
-impaired self0care skills
-diff in making things (constructional apraxia)
- denial of deficits (anosagnosia)
- impaired drawing ability

What patient says does not necessarily indicate how they'll actually perform.

Locus of lesion is not precise.

Front 33

Parietal Lobe Tests

Back 33

- optokinetic nystagmus
- double-simultaneous stim (extinction)
- drawing, block designs
- cross-outs

Front 34

Occipital Lobe

Back 34

Primary Visual Cortex

- unilateral lesion cause CL hemianopsia
- bilateral lesions cause cortical blindness

Visual assoc cortex
-fxn in visual analysis
- lesions may cause visual agnosia -- impairment in recognizing. Test for recognition by matching.

- Alexia w/o agraphia -- inability to xfer info between hemis. L occipital infarct involving splenium of corpus callosum.

Front 35

Temporal Lobe: Primary auditory cortex (Heschl's gyrus)

Back 35

- upper surface of temporal lobe
- tonotopic organization
- each hemisphere responds to stimuli from BOTH ears

Front 36

Auditory association cortex

Back 36

Wernicke's area!

- relates to language perception
- R temporal area relatively quiet (mostly in L). R may fxn in NV memory and music appreciation

Front 37

Seven Components of Wernicke-Geschwind Model

Back 37

Brocas Area

Primary Motor Cortex

Arcuate fasciculus

Primary auditory cortex

Wernicke's area

Angular gyrus

Primary visual cortex

Front 38

Conduction Aphasia

Back 38

Can't repeat back.

Damage to arcuate fasciculus disrupts repetition of speech sounds.

Front 39

Sensory receptors

Back 39

TYpes:
- mechanoreceptive (touch, pressure, vibration, position)
- thermoreceptive (hot and cold)
- nociceptive (pain)

Meissners, Ruffini's, Golgi, Pacinian, etc

Front 40

Adaptation

Back 40

Pain nerves -- nonadapting (free nerve ending)

Pressure -- slowly adapting (merkel discs,ruffini corpuscles)

Vibration -- rapidly adapting (Pacinian corpuscles)

Front 41

Two systems of somatosensory pathways

Back 41

1. Dorsal columns -- FINE DISCRIM TOUCH, position, vibration


2. Ventral-Lateral system -- pain, temp, general touch
(pain and temp - lateral; touch - anterior