cerebral cortex and subcortical structures

gray vs. white matter in the cortex

• gray matter

  • more superficial

• white matter

  • deeper, more internal (opposite than SC)

what do we already know?

brodman’s areas

• different areas of cortex have different arrangements of these layers (difference cells) —> different functions

• Korbinian Brodmann inferred function based on organization

cortical columns

• all sensory systems are organized in a column network

  • cells in vertical cluster that are selective for the same receptive field attribute

• somatotopic organization

• larger cortical representation for areas with smaller receptive fields

frontal lobe

• M1 —> start of CST

• Broca’s area

  • left: motor output of speech

  • right: prosody (flection, tone, emotion) of speech

• FEF

  • conjugate (both eyes together) contralateral gaze

• premotor area

  • sensory motor integration

  • initiation of motor action

  • externally guided motor planning (external cues)

• supplementary motor area

  • memory guided movements (ex. typing)

  • bilateral tasks

  • internally guided motor planning

• premotor and supplementary motor areas are DRIVERS of CST

• dorsal lateral prefrontal cortex —> sensitive to cortisol

  • executive functions, attention, problem solving

• orbital frontal cortex

  • limbic connections

  • social behaviors

  • reward judgements (delaying)

parietal lobe

• S1 (STT and DCML end)

• association areas

  • everything that isn’t S1

    • integration of inputs

• wernicke’s area

  • left: language comprehension

  • right: music, understanding prosody of speech

• angular gurus

  • spatial cognition

  • left/right discrimination

  • math

    • lateralized to left

• dorsal stream

  • where you are in space/how to move in space — PRAXIS

    • parietal stroke = apraxia

temporal lobe

• wernicke’s area

  • comprehension of speech

• A1 (auditory) —> close to language comprehension (wernicke’s area)

• parahippocampal gyrus

  • entorhinal cortex

    • spatial

  • hippocampus deep within

  • Papez circuit

  • early signs of dementia found here (degeneration)

• uncus

  • increase in intracranial pressure —> uncus herniates

• fusiform gyrus —> facial recognition

• ventral stream —> object recognition/identification

occipital lobe

• V1

• association areas

clinical connection - watershed infarcts (aka border zones)

*occur when lack of good blood flow at distal ends of blood supply

• occurs with extremely low blood pressure

• ischemic lesions that occur at the junctions of 2 major arteries

• decreased perfusion in the distal ends of vascular territories

  • low flow states (most common cause)

• cortical border zones

  • cortical gray matter

  • signs of cortical watershed infarct

    • proximal weakness

    • visual perception/higher order processing issues

    • memory impairment

    • higher order cognitive loss

• subcortical border zones

  • basal nuclei —> motor disorder, oculomotor disorder, limbic disorder, cognitive disorder (parallel loops)

  • hippocampus/hippocampal gyrus

    • memory impairment

insular cortex

• not well understood

• integrates information to develop awareness of self

• awareness of our bodies, emotions, perceptions of self

• insular differences in diverse conditions

  • ASD

  • AD

  • schizophrenia

  • avoidant behaviors

    • chronic pain, chronic vertigo

limbic/lobe system

• extensive network of cortical and subcortical structures

  • largely located around corpus callosum —> “rim”

• complex functions involved in response to emotions/stress and affective behaviors

  • learning and memory

  • autonomic responses

  • endocrine responses

amygdala

• almond shaped nuclei deep in temporal lobe

• considered subcortical structure

• contributes to behavior changes in response to

  • stress

  • learned behaviors based on reward/punishment

  • fear conditioning

• input from

  • VTA —> ventral tegmental area

    • dopamine

  • raphe nuclei

    • serotonin

hippocampus

• deep in temporal lobe, considered subcortical structure

• key role in consolidation of learning and memory

  • declarative memory —> NOT motor memory

• consolidation is the “offline” process of making memories relatively stable (when hippocampus is most active)

cingulate gyrus/cortex

• described as part of limbic system

  • anterior cingulate cortex

    • emotions

      • endocrine and autonomic response

    • reward-based cognitive decision making (willpower)

    • motor behaviors in response to emotional state

  • posterior cingulate cortex

    • visuospatial orientation

    • imagination

    • episodic memory formation

updated Papez circuit

emotions are…

• temporary change in affect of feeling state

• elicited by affectively salient situations

• involve multiple systems

  • physiology

  • brain activity

  • behavior

  • conscious experience

• result in:

  • adaptive behavior responses

    • approach or avoidance (hypothalamus)

subjective experiences of emotion

• not just amygdala

  • significant projections to the cortex

  • hypothalamus

    • visceral responses

  • basal ganglia/nuclei

    • process emotions

• cortical structures are integral

  • medial orbital frontal (supplied by ACA)

    • implicit motor actions

    • explicit conscious processing

      • reward

      • avoid punishers

      • implement long term plan, reward delay

emotional theories and neural presentation

• basic emotion theories

  • basic emotions have a distinct representation or circuity in the brain

    • fear circuit or location

    • happiness circuit or location

• dimensional emotion theories

  • emotions occur through a combination of pathways, activating in different way and amounts

    • dependent on context

    • arousal and valence levels

cortical white matter pathways

• superior longitudinal fasciculus —> damage = aphasia

• inferior longitudinal fasciculus

• cingulum

• corpus callosum (largest white matter pathway)

alien hand syndrome

• rare syndrome marked by involuntary and uncontrollable motor behaviors

  • self injuries

  • deny ownership of body part —> “that is not my hand”

  • function

  • conflict —> right hand does an action, left hand directly stops right hand from doing action

traumatic brain injury — diffuse axonal injury

• primary injury

  • localized injury

  • skull fracture compressing brain tissue

  • coup-contra coup

• diffuse axonal injury

  • secondary

  • shearing or tearing of axons from contra-coup disrupts/destroys function

• diffuse is a misnomer

  • midline white matter

    • corpus callosum

    • internal capsule

    • brain stem white matter

    • cerebellar peduncles

central processing

• meaning is constructed by integrating information from all modalities

  • the layers of the cortex allow for communication between lobes and areas

• context matters

  • central processing activates limbic/motor centers

  • the light tickle of a feather or spider crawling on you may be the same but the behavioral responses approach will be very different —> due to limbic and motor centers

additional vestibular pathway connections

• reticular activating system

• emetic pathway —> vomiting

subcortical processing

• cerebellum

  • the vestibular reflexes can function without cerebellar input, however will be uncalibrated and ineffective

  • damage to vermis (medial zone) impacts the vestibulospinal reflex

    • truncal and gait ataxia

  • damage to Cb impacts VOR

    • loss of gaze stabilization

extrapyramidal descending pathways

subcortical processing (emetic pathway)

• vestibular input to emetic centers

  • vomiting

• area postrema

  • circumventricular organ

  • able to detect toxins in blood via chemoreceptors

• conflicting visual and vestibular info can cause nausea/vomiting

  • thought input from vestibular nuclei “dumps” excess neurotransmitters into the area postrema mimicking poisoning and triggering vomiting

    • dopamine, histamine, serotonin

cortical processing

• no primary vestibular cortex

  • integrated with somatosensory and visual inputs to develop sense of self in space and self in motion in space

• major areas

  • parietal-insular vestibular cortex

    • posterior insula

    • inferior parietal lobe

  • superior temporal cortex

  • right hemisphere dominant

  • reciprocal inhibitory feedback between PIVC and visual cortex

  • descend with CST to spinal cord

    • influence postural adjustments