Thalamus and Cerebral Ctx Cerebral Cortex

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Thalamus and Cerebral Ctx Cerebral Cortex Powered By Docstoc
					                                                                                  Thalamus and Cerebral Ctx
Cerebral Cortex                                                                                 Columnar organization of cortex
Layers of cortex                                                                                 Primary sensory areas are organized in vertical column arrays  “microprocessing” of a
                                                                                                    single piece of information
      Type                Seen in…                # Layers             Features
                                                                                                 Example: ocular dominance columns seen in V1  input to a column comes from a single
  Neocortex      >90% human + primate ctx         6            What we are learning about!          area of a monocular visual field  same idea for other sensory inputs
                 “Lower” animals
  Archicortex                                     3            “First cortex”                    Slower than a laptop, but we have a lot more microprocessors!
                 Humans = hippocampus
                 Rodents, cats                                                                  Types of fibers found in cortex
                                                               “Old ctx” – transitional
  Paleocortex Humans: subiculum of                4-5                                           Associational fibers: connect cortical areas w/in same hemisphere from lamina 3
                                                               between archi and neo
                 parahippocampal gyrus                                                           Cingulum: interconnects cingulate gyrus + parahippocampal gyrus
Neocortical layers                                                                               Superior longitudinal (arcuate) fasciculus: Wernicke’s (language comprehension) 
Major neuronal cell types:                                                                          Broca’s (language production)
 Pyramidal cells: ~pyramidal shape, long dendrite to apical surface (seen in EEG activity)      Uncinate fasciculus: limbic areas (septal + uncus)
 Granule (stellate) cells – look like starbursts                                                Superior, inferior occipitofrontal fasciculi: interconnect visual areas w/frontal assoc ctx
                                                                                                Commissural fibers: project to homologous areas in opposite hemisphere from lamina 3
                                                                                                 Corpus callosum: interconnects most of cerebral ctx except portions of temporal lobe
                                                                                                 Anterior commissure: superior temporal lobes
                                                                                                 Posterior commissure: (really part of brainstem but don’t forget it): cross over of pretectal
                                                                                                   neurons in pupillary light reflexes
                                                                                                 Hippocampal commissure
                                                                                                Projection fibers: project to subcortical areas, including thalamus from lamina 5
                                                                                                 Corticospinal                           Corticobulbar
                                                                                                 Corticothalamic                         Corticostriatal

                                                                                                                                       “The Big Picture”

                                                                                                                                                                                Cortical activity =
                                                                                                                                                                                 “what we are
         Lamina              Info flow                     Connections…                                                                                                            aware of”
I     Molecular layer         Afferent    Brainstem monoamine neurons
II    External granular       Afferent    From other areas of ctx (lamina III)
                                          To other areas of ctx (lamina II)
      External pyramidal                  o Association axons in same hemisphere
III                           Efferent
      cell layer                          o Commissural axons: intracortical, connect
                                               homologous regions of hemispheres
IV    Internal granular       Afferent    From thalamus + brainstem
                                                                                                                                   Approximate areas of
                                          Projection axons to various subcortical                                                     sensory cortex:
V     Internal pyramidal      Efferent
                                          structures (BG, brainstem, corticospinal fibers)                                            Somatosensory
VI    Multiform layer         Efferent    To thalamus (corticothalamic neurons)                                                            Visual
 Lamina II-VI have intercommunicating projections to each other as well
 ALSO: neuromodulatory input from midbrain (DA, NE, 5-HT) – bypasses thalamus                                                    Gustatory (insula + frontal
 Size of each lamina varies by area of ctx  ex. higher areas have > II, input areas > IV                                        ~somatosensory for face)
                                                                                 Thalamus and Cerebral Ctx
Functional areas of cerebral cortex
General concepts:                                                                              Cerebral lateralization: functions/processing performed using one hemisphere only
 Ascension = ↑ sophistication of processing                                                   Usually left hemisphere:                          Usually right hemisphere:
 Highest level unimodal sensory ctx = processing of sensory info, memory storage               Language (100% R handed folk, can be             Attention
 Multimodal = integration                                                                         opposite/mix in lefties)                       Spatial skills
 Proportions of ctx dedicated to different areas in diff species is fairly equal … EXCEPT:     Praxis                                           Music + prosody (“music of language,”
 Higher association ctx – humans have LOTS “where we actually think, process,                  Computational skills                                aka inflection)
   ruminate” – the “10% of our brain that we use”???
                                                                                               Syndromes of cortical dysfunction
Association cortex:
                                                                                                  Syndrome                            Features                         Lesion site in cortex
 Higher assoc ctx – higher cognitive functions, memory storage, multimodal                                          Inability to recognize objects; despite
 Highest levels of association ctx = posterior portion of parietal lobe + prefrontal cortex                         intact sensory inputs (different from
    o Appreciation of consequences of actions, impulse control, conceive of future             Agnosia                                                           2º visual cortices
                                                                                                                     anomia – can recognize object, but
 Lesions = changes in personality, social behaviors, ability to control impulses, loss of                           cannot name)
    appreciation for consequences of actions
                                                                                                  Tactile agnosia    Cannot recognize using only hands           Unilateral 2º somatosensory
 Examples:
    o Phineas Gage: pipe through frontal lobe  major personality ∆s, lack social ability         Visual agnosia     Cannot visually recognize                   Unilateral 2º visual
    o Dr. Ciment’s dog Simon: no prefrontal ctx (like all dogs), lack of impulse control                             Cannot recognize that have a sensory
                                                                                                  Anosognosia                                                    Higher association
Limbic cortex: memory, olfaction, emotion (much more on this in limbic system lecture!)                              deficit (ex. unaware of blindness)
                                                                                                  Prosopagnosia      Cannot recognize faces (only)               3º visual
Primary motor cortex:
 Contralateral movements of individual joints                                                                                                                   2º (pre-motor)
                                                                                                                     Cannot perform repetitive stereotyped
                                                                                               Apraxia                                                           (or corpus callosum: unilateral
 Lesion = spastic hemiparesis                                                                                       mvments; preserve sensory, motor fxn
                                                                                                                                                                 “instructions” for praxis)
Secondary motor cortex (premotor):
                                                                                               Aphasia               Inability to use language                   Various
 Multiple joints, temporal aspects of complex movements
 Higher areas = praxes (repetitive motor activities throughout days)                            Expressive
                                                                                                                     Inability to form spoken/written words      Broca’s area
Primary sensory cortex:                                                                          Receptive           Inability to understand language, can
 Unilateral input from contralateral body, columnar organization                                                                                                Wernicke’s area
                                                                                                 (Wernicke’s)        produce words but don’t make sense
 Example 1º visual ctx: on center/off center information                                                            Wernicke’s speech pattern, but intact
Secondary sensory cortex (aka HIGHER sensory ctx)                                                Conductive                                                      Superior longitudinal (arcuate)
                                                                                                                     comprehension; cannot repeat
                                                                                                 aphasia                                                         fasciculus
 Bilateral input from 1º sensory ctx                                                                                sentences
 Analyze spatial + temporal relationships of 1º sensory info                                                        Inability to perceive + attend to objects   Superior parietal lobule of R
 Example: 2º visual ctx: lines – of contrast, illumination, color, movement                                         in a particular spatial region              hemisphere (high level sensory)
 Lesion = agnosias
 3º sensory: forms, objects in space                                                          Objective not covered in lecture or syllabus:
                                                                                               Describe the physiological properties of the following types of cortical neurons:
Dominance and Lateralization                                                                   "attention neurons"; "planning neurons"; "recognition neurons"
Cerebral dominance (handedness): functions are performed using either hemisphere, but
individual “prefers” to use one hemisphere + performs better
 Writing, ball throwing
 Usually left hemisphere is dominant
 90% of individuals have dominant hand
 Some genetic component hypothesized  100% infants have larger planum temporale
      (A1 cortex - Heschle) on L than R

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