Sensorimotor systems Learning, memory

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Sensorimotor systemsLearning, memory amnesia

• Chapters 8 and 11

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Three principles of sensorimotor function

• hierarchical organization
• Two other organizing characteristics?
• motor output is guided by sensory input
• The case of G.O. darts champion
• The exception?
• learning changes the nature and locus of
  sensorimotor control

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Posterior Parietal Association Cortex

• Function Integrates of sensory information to
  plan and initiate voluntary movement and
  attention.
• Sensory system inputs visual, auditory and
  somatosensory.
• Outputs dorsolateral PFC, secondary motor cortex
  and frontal eye fields.

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Dorsolateral PFC
Frontal eye field
Auditory cortex
Visual cortex
Inputs to Posterior Parietal Association Cortex
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Dorsolateral PFC
Frontal eye field
Auditory cortex
Visual cortex
Outputs to Posterior Parietal Association Cortex
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Damage to the Posterior Parietal Association
Cortex

• Can produce a variety of deficits
• Attention
• Perception and memory of spatial relationships
• Reaching and grasping
• Control of eye movements

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Damage to the Posterior Parietal Association
Cortex

• Apraxia a disorder of voluntary movement not
  attributable to a simple motor deficit (weakness
  or paralysis) or to a deficit in comprehension or
  motivation.
• Results from unilateral damage to the left
  posterior parietal cortex.

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Damage to the Posterior Parietal Association
Cortex

• Contralateral neglect a disturbance in a
  patients ability to respond to stimuli on the
  side of the body contralateral to a brain lesion
  (not a simple sensory or motor deficit).
• Often associated with large lesions of the right
  posterior parietal lobe.

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Dorsolateral Prefrontal Cortex

• Function plays a role in the evaluation of
  external stimuli and initiation of voluntary
  responses to those stimuli.
• Main input posterior parietal cortex
• Outputs secondary motor cortex
• primary motor cortex
• frontal eye fields

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Dorsolateral Prefrontal connectivity
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Dorsolateral Prefrontal cortex

• Neurons in this area respond to the
  characteristics of objects (e.g., color/shape),
  the location of objects or to both.
• The activity of other neurons is related to the
  response itself.

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Secondary motor cortex

• Input most from association cortex
• Output primary motor cortex
• Two classic areas
• SMA
• Premotor cortex

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Secondary Motor Cortex

• Current classifications suggest
• At least 7 different areas
• 3 supplementary motor areas
• SMA and preSMA andSupplementary eye field
• 2 premotor areas
• PMd and PMv
• 3 cingulate motor areas
• CMAr, CMAv and CMAd

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Secondary Motor Cortex

• Subject of ongoing research
• In general, may be involved in programming
  patterns of movements based on input from PFC
• Mirror neurons in premotor cortex (also in
  posterior parietal cortex) are involved in social
  cognition, theory of mind and may contribute to
  autism if dysfunctional.

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Primary Motor Cortex

• Precentral gyrus of the frontal lobe
• Major point of convergence of cortical
  sensorimotor signals
• Major point of departure of signals from cortex
• Somatotopic more cortex devoted to body parts
  which make many movements

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Motor homunculus
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Primary Motor Cortex

• Monkeys have two hand areas in each hemisphere,
  one receives feedback from receptors in skin.
• Stereognosis recognizing by touch requires
  interplay of sensory and motor systems
• Damage to primary motor cortex
• Movement of independent body parts (e.g., 1
  finger)
• Astereognosia
• Speed. accuracy and force of movement

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Other sensorimotor structures outside of the
hierarchy

• (sometimes called extrapyramidal systems)
• Cerebellum
• Basal ganglia
• both modulate and coordinate the activity of the
  pyramidal systems by interacting with different
  levels of the hierarchy.

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Cerebellum

• 10 of brain mass, gt 50 of its neurons
• Converging signals from
• primary and secondary motor cortex
• brain stem motor nuclei (descending motor
  signals)
• Somatosensory and vestibular systems (motor
  feedback)
• Involved in motor learning, particularly
  sequences of movement
• Damage to cerebellum disrupts direction, force,
  velocity and amplitude of movements causes
  tremor and disturbances of balance, gait, speech,
  eye movement and motor sequence learning .

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Basal Ganglia

• A collection of nuclei
• Part of neural loops that receive cortical input
  and send output back via the thalamus
  (cortical-basal ganglia-thalamo-cortical loops)
• Modulate motor output and cognitive functions
• Cognitive functions of the basal ganglia

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Descending Motor Pathways

• Two dorsolateral
• Corticospinal
• Corticorubrospinal
• Two ventromedial
• Corticospinal
• Cortico-brainstem-spinal tract
• The corticospinal tracts are direct pathways

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Dorsolateral Vs Ventromedial Motor Pathways

• Ventromedial
• one direct tract, one that synapses in the brain
  stem
• More diffuse
• Bilateral innervation
• Proximal muscles
• Posture and whole body movement

• Dorsolateral
• one direct tract, one that synapses in the brain
  stem
• Terminate in one contralateral spinal segment
• Distal muscles
• Limb movements

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Experiments by Lawrence and Kuypers (1968)

• Experiment 1 bilateral transection of the
• Dorsolateral (DL) corticospinal tract
• Results
• monkeys could stand, walk and climb
• difficulty reaching but improved over time
• could not move fingers independently of each
  other or release objects from their grasp.

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Experiments by Lawrence and Kuypers (1968)

• Experiment 2
• The same monkeys with DL corticospinal tract
  lesions received 1 of 2 additional lesions
• The other indirect DL tract was transected
• Both ventromedial (VM) tracts were transected

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Experiments by Lawrence and Kuypers (1968)

• Experiment 2 Results
• The DL group could stand, walk and climb but
  limbs could only be used to rake small objects
  of interest along the floor
• VM group had severe postural abnormalities great
  difficulty walking or sitting. Although they had
  some use of the arms they could not control their
  shoulders.

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Experiments by Lawrence and Kuypers (1968)

• Conclusions
• the VM tracts are involved in the control of
  posture and whole-body movements
• the DL tracts control limb movements (only the
  direct tract controls independent movements of
  the digits.

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The case of H.M.

• Intractable epilepsy
• one generalized convulsion each week
• Several partial convulsions each day
• 1953 surgery Bilateral medial temporal lobectomy
• temporal pole
• amygdala
• entorhinal cortex
• hippocampus

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Corkin et al. (1997)
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Corkin et al. (1997)
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Effects of Bilateral Medial Temporal Lobectomy

• Convulsions were dramatically reduced
• IQ increased from 104 to 118
• Short-term memory (STM) intact
• Temporally-graded retrograde amnesia
• Severe anterograde amnesia

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Amnesia

• Retrograde (backward-acting) unable to remember
  the past
• Anterograde (forward-acting) unable to form new
  memories
• While H.M. was unable to form most types of new
  long-term memories, his STM was intact

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• Mirror-drawing task
• H.M.s performance improved over 3 days (10
  trials/day) despite the fact that he could not
  consciously remember the task on days 2 and 3.

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• Rotary-Pursuit Test
• H.M.s performance improved over 9 daily practice
  sessions again, with no recognition of the
  experience

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Explicit vs Implicit Memories

• Explicit memories conscious memories
• Implicit memories unconscious memories
• Repetition priming tests were developed to assess
  implicit memory performance

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Incomplete pictures test
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Implications of H.M.s amnesia

• Medial temporal lobes are involved in memory
  formation.
• STM and LTM are dissociable H.M. is unable to
  consolidate certain kinds of explicit memory.
• the fact that he could form some memories
  suggests that there are multiple memory systems
  in the brain.

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Medial Temporal Lobe Amnesia

• Not all patients with this form of amnesia are
  unable form new explicit long-term memories, as
  was the case with H.M.
• Two kinds of explicit memory
• Semantic memory (general information) may
  function normally while episodic memory (events
  that one has experienced) does not they are
  able to learn facts, but do not remember doing so
  (the episode when it occurred)

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Vargha-Khadem et al., (1997)

• Studied three children that had bilateral
  temporal lobe damage early in life.
• Like H.M., the children could not form episodic
  memory, however they did acquire reasonable
  levels of factual knowledge and language ability
  in mainstream school.

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Effects of Cerebral Ischemia on the Hippocampus
and Memory

• R.B. suffered damage to just one part of the
  hippocampus (CA1 pyramidal cell layer) and
  developed amnesia
• R.B.s case suggests that hippocampal damage
  alone can produce amnesia
• H.M.s damage and amnesia was more severe than
  R.B.s

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Object-Recognition Memory

• Early animal models of amnesia involved implicit
  memory and assumed the hippocampus was key
• 1970s monkeys with bilateral medial temporal
  lobectomies showed LTM deficits in the delayed
  nonmatching-to-sample test
• Like H.M., performance was normal when memory
  needed to be held for only a few seconds (within
  the duration of STM)

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Delayed nonmatching-to-sample task pretend youre
the monkey
Sample stimulus touch it and get a yummy treat
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10 min delay during which other sample stimuli
are presented
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Choice phase pick the image that is new
Another yummy treat
Darn, no food
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Testing object-recognition memory
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Medial temporal lobe (MTL)
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Delayed non-match to sample results
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The Mumby Box
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Object recognition in rats
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Comparison of lesions in monkeys and rats
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Neuroanatomy of object recognition

• Bilateral removal of the rhinal cortex
  consistently results in object-recognition
  deficits.
• Bilateral removal of the hippocampus produces
  moderate deficits or none at all.
• Bilateral removal of the amygdala has no effect
  on object-recognition.

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Is the hippocampus involved in object recognition
memory?

• The Case of R.B. suggests that the lesions of the
  CA1 region of the hippocampus (due to ischemia)
  can produce severe memory deficits
• Ischemia in animal models also produces deficits
  in object recognition
• Yet deficits in object recognition are only
  moderate to non-existent in other animal lesion
  models
• Why?

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Mumby et al. (1996)

• Bilateral hippocampectomy actually blocks the
  damage produced by ischemia!
• Explanation
• Ischemia causes hippocampal neurons to release
  glutamate, which produces damage outside of the
  hippocampus (particularly in rhinal cortex),
  although standard histological techniques do not
  show the damage follow-up functional imaging
  studies have confirmed the dysfunction.

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The Hippocampus

• Rhinal cortex plays an important role in object
  recognition.
• Hippocampus plays a key role in memory for
  spatial location.
• Hippocampectomy produces deficits on Morris maze
  and radial arm maze (Chapter 5)
• Many hippocampal cells are place cells
  responding when a subject is in a particular place

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Theories of Hippocampal Function

• OKeefe Nadel (1978) Cognitive map theory
  constructs and stores allocentric maps of the
  world
• Rudy Sutherland (1992) Configural association
  theory involved in retaining the behavioral
  significance of combinations of stimuli
• Brown Aggleton (1999) is involved in
  recognizing the spatial arrangements of objects

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Synaptic Mechanisms of Learning and Memory

• What is happening within the brain structures
  involved in memory?
• Hebb changes in synaptic efficiency are the
  basis of LTM
• Long-term potentiation (LTP) synapses are
  effectively made stronger by repeated stimulation

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Long Term Potentiation (LTP)
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Cross-section of the NMDA receptor complex