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Lecture 18

HMB200 2014 Lecture 18.pdf

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Human Biology
John Yeomans

  Lecture  18:  Cortex  –  From  Limbic  to  Association   Ventral:  towards  the  belly   Cortex  Types  (first  categorized  by  Brodmann)   Dorsal:  towards  the  back   -­‐ paleocortex  (basal  forebrain)   Rostral:  towards  the  head   o older  areas  of  cortex   Caudal:  towards  the  tail   o thin,  about  only  3  layers     Anterior:  towards  the  front   -­‐ transitional  cortex  (subiculum)   Posterior:  towards  the  rear   o older  cortex   o thin,  about  only  4  layers   -­‐ association  cortex  (frontal  cortex,  Broca’s  area,  vernica’s  area,  temporal  lobe)   o modality  specific  visual  or  motor  areas   à  associated  with  one  sensory  system   o thick  cortex,  less  layering,  lots  of  cells   o less  defined   -­‐ primary  cortex  (visual)   o distinct  layering   o primary  areas  are  easy  to àse  have  nice  layers   § layer  1:  myelinated  axons  in  the  outer  layers  (connect  between  cortical  regions )   • no  cells  in  layer  1   § layer  2  and  3:  small  cells  for  cortical  processing   • these  cells  send  their  axons  out  in  layer  1   § layer  4:  primary  visual  cortex   • thick  in  sensory  areas,  thin  in  motor  areas   • have  strong  sensory  input  from  the  thalamus   § deepest  layers:  large  pyramidal  cells  (especially  large  in  motor  cortex)     • provide  motor  output  of  cortical  spinal  tract   • motor  output  going  down  back  to   thalamus  (deep  brain  areas)  AND  subcortical  regions  to   pons  and  spinal  cord  (cortical-­‐cortical  areas)     Anatomical  Definitions   -­‐ Brodmann’s  Areas  (1-­‐42)   -­‐ Paleocortex:  3  layers   o Oldest  form  of  cortex   o Includes  basal  forebrain,  olfactory  cortex   o 3  distinct  layers,  relative ly  thin  cortex   -­‐ Transitional  cortex   o Transition  from  3 à 6  layers   o Allocortex  to  juxtallocortex  as  u  go  from  3  to  6  layers   o Includes  parahippocampal  and  hippocampal  cortex,  and  many  limbic  areas   -­‐ Limbic:  Visceral  inputs  (taste,  olfaction,  hypothalamus,  dopamine).   o Limbic  cortex  includes  paleocortex,  transitional  cortex,  and  even  some  associate  neocortex   o High  variable   o Limbic  cortex  varies  in  thickness  and  cortical  type   o Cuts  across  all  areas   o Limbic  is  defined  by  types  of  inputs,  not  by  thickness   o If  inputs  are  taste  and  olfaction,  if  they  include  hypothalamic  and  dopamine  projections  =  limbic   -­‐ Primary  neocortex:  Somatic  inputs  from  thalamus.  Layers  4  and  5  dominate.   o Specific  input  from  1  somatosensory  input   à  comes  directly  from  sensory  areas  of  the  thalamus   o In  these  areas,  layers  4  and  5  dominate   o Layer  4  dominates  sensory  cortical  areas     o Layer  5  dominates  primary  motor  cortex  regions   -­‐ Association  neocortex:  Cortical  and  non-­‐primary  thalamus  inputs  (mediodorsal  n,   pulvinar)       Evolution  of  Cerebral  Cortex   -­‐ Subcortex   • Includes:  basal  ganglia,  extended  amygdala,  striatum     • No  cortex?  Subcortical   • Subcortical  extended  amygdala  –  areas  with  no  clear    s -­‐ Paleocortex       • Includes:  basal  forebrain,  olfactory  cortex   • Have  3  thin  layers   -­‐ Archicortex  &  transitional  (juxtallocortex)   •  Includes:  medial  prefrontal,  insular  cortex,  hippocampus   • older  cortical  area  where  you   transition  from  3  to  6  layers   -­‐ Limbic  cortex   • orbitofrontal,  cingulate,  parahippocampal   -­‐ Primary  neocortex   • Motor,  somatosensory,  visual,  auditory.   -­‐ Association  neocortex   • Frontal,  Parietal,  Temporal     Speech  and  Language   -­‐ localized  to  left  hemisphere   -­‐ humans  have  speech  function  in  left  hemisphere,  develops   early  (prenatal)   -­‐ left  hemisphere  is  critical  for  speech  in  97%  of  humans   -­‐ damage  to  left  hemisphere  à  several  areas  with  speech  deficits     Bird  Song  and  Left  Hemisphere   -­‐ bird  song  is  generally  located  in  the  left  forebrain   of  the  bird   -­‐ the  Zebrafish  is  the  only  bird  that  song  learning  is   in  right  hemisphere   -­‐ left  forebrain  is  adequate  for  speech  only  in  the   spring  time  for  some  birds   • sings  in  spring  time  when  testosterone   stimulates  the  growth  of  neurons  in  left  cortical   areas   -­‐ Hyperstriatum,  ventrale ,  and  RA  (robust  nucleus   of  the  arcopallium)  region  develop  in  spring  to   create  song  learning  in  young  male  canaries   • Learn  song  from  parents,  they  develop   new  cortical  areas  in  the  Hyperstriatum,   ventrale,  and  RA  for  song  motor  function     Human  Aphasias  (speech  problems)   • 97%  of  those  with  speech  problems  have  left  hemisphere  injury   • only  those  who  are  left  handed,  and  have  speech  organized   in  right  hemisphere  à  right  hemisphere   damage  leads  to  aphasia   • most  left  handers  also  have  speech  organized  in  left  hemisphere  too   • Broca’s  Tan.  “No  ifs,  ands,  or  buts”   • Damage  to  motor  association  area  in  front  of  the  motor  areas  of  the  left  hemisphere  =  areas  where   damaged  resulted  in  inability  to  speak       • Small  injury  in  left  frontal  cortex  =  patient  couldn’t  produce  any  words  except  2  :  “tan”  and  a  swear  word   • Patient  called  Tan  said  the  word  “tan”  repeatedly     • Produce  distinct  gestures  to  communicate  to  other s   • When  he  got  frustrated,  he  would  emit  a  swear  word   rd • Injury  to  speech  area  was  in  3  convolution  in  the  frontal  lobe   • People  with  Broca’s  aphasia  have  injury  to  frontal  region  (in  the   ventral  frontal  lobe,  just  in  front  of  the  motor   area  for  moving  of  the  face)  à  motor  area  for  speech  production   • Individuals  have  little  spontaneous  speech   -­‐  if  they  do,  its  non-­‐fluent  speech   • Understanding  of  speech  is  not  affected     • Speech  production  is  poor,  speech  comprehension  is  excellent   • Difficult  repeating  words ,  even  if  they  understand  the  word   • Difficulty  naming  objects  (pointing  to  objects  named)   • Wernicke’s  Aphasia .  Lots  of  meaningless  words.  Poor  understanding,  and  recovery   • Discovered  damage  to  another  brain  area  is  important  for  the  understanding  of  speech   • Temporal  lobe  surrounding  A1  (auditory  association  area  à  large  region  surround  primary  auditory   area  located  mainly  inside  the   Sylvain  Fissure)     • This  large  auditory  association  area   extends  out  to  temporal  lobe  from  the  shelf  of  the  top  of  the  Sylvain   fissure   • These  individuals  have  fluid  speech  à  produce  LOTS  of  words  (meaningless  words)  and  poor   comprehension   • Wernicke’s  Theory  of  Speech  and  Reading.   • Speech  is  learned  by  way  of  auditory   association  cortex   • When  people  hear  words  (by  primary   auditory  cortex),  information  is   transferred  to  auditory  association  area   (Wernicke’s  area)   • Within  Wernicke’s  area:  learning  of   speech  by  using  the  sounds  to  construct   knowledge  about  words     • How  we  learn  from  mothers   à   constructing  sounds  into  words   • Conduction’s  Aphasia  –  cannot  repeat   • Damage  to  the  connec
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