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HMB200 2014 Lecture 23.pdf

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Human Biology
John Yeomans

  Lecture  23:  Memory  Systems   Memory   • Memories  are  what   make  human  experiences  meaningful.   • Mental  diseases  are  disordered  emotional  memories.   • Life  experiences  are  coded  in  episodes:  episodic  memory   • Dementias  are  global  losses  in  memory.   – Aging:  dementia;  Alzheimer’s  à  long  term  major  loses  in  memory   – When  cortical  systems  are  disrupted,  we  cannot  reconstruct  memories  of  our  lives   – Dementia:  aging  related  losses  of  memory  that  are  widespread  loses  due  to  widespread  forebrain  or   cortical  damage   • Amnesias  are  more  specific  losses   – Memory  loss  after  injury:  retrograde  amnesia   – Loss  of  memory  after  injury:  anterograde  amnesia       Types  of  Memory   • Reflexes,  fear/anxiety,  habits,  speech,  spatial,  life  episodes,  etc.,  all  learned  and  remembered  in  separate  brain   areas—Parallel  systems.   • Declarative  vs.  Non-­‐declarative.  Explicit  (“conscious”)  vs.  Implicit  (“unconscious”)   – Declarative  memories:  life  experiences  (facts  and  figures  of  events  in  our  lives)   à  we  are  aware  of  and   think  about  =  part  of  conscious  experience  (E xplicit  –  can  talk  about  =  aware  of  it)   – Undeclarative  memories:  also  called  procedural  memories  (reflex  memories,  habit  memories,   performances  of  skills)  à  things  we  are  less  aware  of  (implicit)   • There  are  procedural  memories  that  are  explicit   or  implicit   • Short-­‐term  (e.g.  working)  vs.  Long-­‐term.   • All  learned  and  remembered  in  separate  brain  areas:  parallel  systems     Types  of  long  Term  Memory     • Declarative:   § Frontal  Lobe:  Life  History  and  Plans   o Episodic  memories:  facts  and  verbal  thoughts   § Stored  in  frontal  lobe  (dorsal  lateral  cortex  for  episodic  memories)     § places  +  faces  =  series  of  events  of  our  life  story   § life  history  is  organized  in  pre-­‐frontal  area  (life  history  is  constructed  here)   § more  associated  with  left  hemisphere  and  temporal  lobe   o Semantic:  associated  with  speech  areas  of  left  cortex   § Left  Speech  Cortex:  Semantic  memories   § front  lobe  and  pre  frontal  lobe  for  planning   § Can  be  many  forms  (faces,  objects)   • Procedural   o striatum  and  basal  ganglion  –  important  for  remembering  where  to  go  OR  performing  specific  tas ks   o striatum  important  in  compulsive  acts  (OCD)   –  performing  repeatedly     §  involve  habit  memories  and  performances  that  involve  basal  ganglia   § habit  learning   o cerebellum  is  important  in  reflex  learning   § Cerebellum:  Reflex  Delay  Conditioning       § performance  of  motor  movements   § modifications  of  movements  in  reflex  learning  =  Pavlovian  learning   o Hippocampus  and  Temporal  Lobe:  Formation  of  Experiences  and  Emotions   § Hippocampus  involved  in  different  types  of  conditioning  than  cerebellum   § Cerebellum:  important  for  learning  mo tor  reflexes  when  things  are  happening   § Hippocampus:  important  for  learning  associations  of  things  that  are  separated  in  time  ( trace   conditioning)   • Simple  changes  in  procedure  can  change  the  memory  from  being  a  cerebellar  memory   (implicit)  to  a  hippocampal  memory  (explicit)   o Temporal  lobe:  important  for  identifying  faces   § Identifying  faces  (object  memory)  gets  converted  into  emotional  memory   –  occurs  in  left  temporal   association  cortex   • Hippocampus  is  important  in  converting  this  into  emotional  memories   • But  hippocampus  and  medial  temporal  lobe  is  also  important  for  events  (series  of  events   needed  to  create  experiences   –  for  spatial  experiences)   o Medial  temporal  lobe  and  hippocampus:  memories  are  transported  from  sensory   events  à  conscious  experiences  à  long  term  permanent  memories   § Faces  and  events  can  lead  to  emotions   o Parietal  Lobe:  Predicted  Movements   § Converting  of  hand  and  eye  experiences  into  spatial  memories   § Prediction  of  where  things  are  going   § Parietal  lobe  is  the  movement  area  of  the  brain  that  predicts  where  things  are  going  (by  visual   events,  putting  them  together  in  time  and  space   –  involves  memory  of  where  things  are  going)     Retrograde  Amnesia   • Head  injury  (concussion) à  result  in  loss  of  consciousness  à  transient  amnesia.   • Memories  recover  in  reverse  order  ( i.e.,  older  memories  first).   – Memories  are  fine  until  you  get  close  to  the  event   – As  you  get  closer  and  closer  to  the  event   –  memories  go  blank   – Amnesia  occurs  for  events  before  the  trauma  and  after  the  trauma   • If  you  go  unconscious,  you  will  not  remember  what  happens  after  (anterograde  amnesia)   • Not  awake,  so  of  course  you  wont  remember   – Memories  come  back  in  the   right  order  (1  hour  before…then  30  minutes  before  the  accident)   • Memories  come  back  in  the  order  that  they  are  restored   – Memories  come  back  in  the  revers ed  order:  Older  memories  come  back  first,  then  memories  close r  to   injury  comes  back  last   – Memories  are  different  as  a  function  of  age   – Older  memories  are  less  vulnerable;  new  memories   most  vulnerable   – As  memories  are  formed,  they  become  less  vulnerable,  and  n ot  as  easily  disrupted   – New  memories:  come  back  last,  most  damaged,  hardest  to  recover   • New  memories  are  most  vulnerable  to  cortical  disruption  (electroconvulsive  shock  or  concussion).   – Electrocompulsive  shock  –  disrupt  memories  in  the  brain  in  an  organized  way  for  a  second   – Time  of  memory  is  closely  controlled  to  time  of  shock   – Memories  change  (vulnerable  initially,  as  they  mature,  they  become  more  and  more  stable  and  less   vulnerable  to  injury  à  memories  are  hardening  (consolidation)   • Consolidation  Theory:  Memor ies  change  from  less  stable  to  more  stable  form.   – Fixed  à  permanent  form   – Hippocampus  converting  memories  from  an  electrical  form  (easily  injured)  into  a  more  stable  form   (involving  hippocampal-­‐electrical-­‐chemical  changes,  which  converts  the  memory  over  time  to  a  more  fixed   more,  eventually  into  a  permanent  form)     Anterograde  Amnesia  and  HPC   • Anterograde  amnesia:  unable  to  remember  after  the  trauma,  and  also  sometimes,  inability  to  form  new  memories   • H.M.  has  severe  epileptic  seizures  (temporal  lobe  seizure  tha t  spreads  from  one  temporal  lobe  to  the  other)   – Removed  medial  temporal  lobe  (included  hippocampus,  entorhinal  cortex  (spatial  memories,  olfactory   memories),  and  amygdala  AND  areas  coming  into  the  hippocampus )  à  whole  hippocampal  and   parahippocampal  complex  regions  lost       – No  more  seizures  after  removal,  but  was  never  able  to  form  memories  ever  again  –  severe  anterograde   amnesia   – Declarative  memories  completely  incapacitate   – Can  only  remember  memories  before  removal   • Still  had  short-­‐term  memory  (can  remember  events  that  happened  RIGHT  away)   – But  will  be  forgotten  in  minutes   – Unable  to  store  memories   – Just  distract  him,  and  new  memories  all  go   away  (had  to  maintain  in  immediate  memory)   • Still  had  oldest  memories  à  Permanent  memories  in   neocortex.   • was  still  able  to  lear n  habit  tasks  –  procedural  memory   was  still  intact  (striatum  motor  task  or  cerebellar   reflex  learning)  à  but  cannot  think  or  plan   (procedural)   • Still  could  form  non-­‐declarative  memories:  Reflex   learning  (cerebellum)  and  complex  motor  tasks   &habits  (striatum)  –  automatic  and  procedural   memories,  cannot  think  about  it   • Hippocampus  required  for  formation  of  new   declarative  memories     • Henry  Molaison  d.  Dec.  2,  2008.   • Difficulty  forming  new  memories  can  happen   • Global  amnesia:  forget  name     Consolidation  and  Long-­‐Term  Storage   • Hippocampus  establishes  time,  place,  context  needed   to  convert  short  term  to  long  term  declarative  memory   • Hippocampus  important  for :   1) analysis  and  consolidation  of  memories ,  THEN   2) conversion  of  these  memories  into  a  more  permanent -­‐gene-­‐transcription  dependent  memory   3) eventually,  the  hippocampus  is  also  able  to  take  those  late  phase -­‐protein-­‐synthesis-­‐dependent  memories,  and   convert  it  into  permanent  memories,  which  are  then  put  into  long  term  cortical  storage   Three  Steps:   1. short  term  consolidation   2. conversion  to  permanent  growth  within  the  hippocampus   3. conversion  into  cortical-­‐long-­‐term-­‐permanent  memory   • 2  stages  of  conversion:   1) conversion  of  events  into  a  more  consolidated  form  (more  stable  form)   – early  stage  in  which  electrical  activity  in  the  hippocampus  g ets  converted  into  kinase  memories  (involves   strengthening  of  synapses)   – early  phase  of  hippocampal  storage   2) conversion  of  short  term  storage  into  long  term  permanent  growth   – long  term  permanent  growth  involves  new  proteins  and  synthesis  of  it   – Hippocampal  damage  does  not  effect  permanent  memories   – Does  not  block  long  term  storage   • Two  stages:  early  and  late  (protein  synthesis)     – Convert  late  phase  protein  to  long  term  cortical   storage   • After  Hippocampus,  long -­‐term  declarative  memories  are   stored  in  many  different  cortical  areas,  e.g.,  episodes,   knowledge.     •
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