Sensorimotor systems Learning, memory & amnesia Chapters 8 and 11

Sensorimotor systemsSensorimotor systemsLearning, memory & amnesiaLearning, memory & amnesia

Chapters 8 and 11Chapters 8 and 11

Three principles of sensorimotor Three principles of sensorimotor functionfunction

hierarchical organizationhierarchical organizationTwo other organizing characteristics?Two other organizing characteristics?

motor output is guided by sensory inputmotor output is guided by sensory inputThe case of G.O. – darts championThe case of G.O. – darts championThe exception?The exception?

learning changes the nature and locus of learning changes the nature and locus of sensorimotor controlsensorimotor control

Posterior Parietal Association CortexPosterior Parietal Association Cortex

Function: Integrates of sensory information Function: Integrates of sensory information to plan and initiate voluntary movement to plan and initiate voluntary movement and attention.and attention.

Sensory system inputs: visual, auditory and Sensory system inputs: visual, auditory and somatosensory.somatosensory.

Outputs: dorsolateral PFC, secondary motor Outputs: dorsolateral PFC, secondary motor cortex and frontal eye fields.cortex and frontal eye fields.

Frontal eye field

Dorsolateral PFC

Visualcortex

Auditorycortex

Inputs to Posterior ParietalInputs to Posterior ParietalAssociation CortexAssociation Cortex

Frontal eye field

Dorsolateral PFC

Visualcortex

Auditorycortex

Outputs to Posterior ParietalOutputs to Posterior ParietalAssociation CortexAssociation Cortex

Damage to the Posterior Parietal Damage to the Posterior Parietal Association CortexAssociation Cortex

Can produce a variety of deficitsCan produce a variety of deficitsAttentionAttentionPerception and memory of spatial Perception and memory of spatial

relationshipsrelationshipsReaching and graspingReaching and graspingControl of eye movementsControl of eye movements


ApraxiaApraxia – a disorder of voluntary movement – a disorder of voluntary movement not attributable to a simple motor deficit not attributable to a simple motor deficit (weakness or paralysis) or to a deficit in (weakness or paralysis) or to a deficit in comprehension or motivation.comprehension or motivation.

Results from unilateral damage to the left Results from unilateral damage to the left posterior parietal cortex.posterior parietal cortex.


Contralateral neglect Contralateral neglect – a disturbance in a – a disturbance in a patient’s ability to respond to stimuli on the patient’s ability to respond to stimuli on the side of the body contralateral to a brain side of the body contralateral to a brain lesion (not a simple sensory or motor lesion (not a simple sensory or motor deficit).deficit).

Often associated with large lesions of the Often associated with large lesions of the right posterior parietal lobe.right posterior parietal lobe.

Dorsolateral Prefrontal CortexDorsolateral Prefrontal Cortex

Function: plays a role in the evaluation of Function: plays a role in the evaluation of external stimuli and initiation of voluntary external stimuli and initiation of voluntary responses to those stimuli.responses to those stimuli.

Main input: posterior parietal cortexMain input: posterior parietal cortex

Outputs: Outputs: secondary motor cortexsecondary motor cortex

primary motor cortexprimary motor cortex

frontal eye fieldsfrontal eye fields

Dorsolateral Prefrontal connectivityDorsolateral Prefrontal connectivity

Dorsolateral Prefrontal cortexDorsolateral Prefrontal cortex

Neurons in this area respond to the Neurons in this area respond to the characteristics of objects (e.g., characteristics of objects (e.g., color/shape), the location of objects or to color/shape), the location of objects or to both. both.

The activity of other neurons is related to the The activity of other neurons is related to the response itself.response itself.

Secondary motor cortexSecondary motor cortex

Input: most from association cortexInput: most from association cortex

Output: primary motor cortexOutput: primary motor cortex

Two classic areas:Two classic areas:

1)1) SMASMA

2)2) Premotor cortexPremotor cortex

Secondary Motor CortexSecondary Motor Cortex

Current classifications suggestCurrent classifications suggestAt least 7 different areasAt least 7 different areas

3 supplementary motor areas 3 supplementary motor areas SMA and preSMA SMA and preSMA andand

Supplementary eye fieldSupplementary eye field

2 premotor areas 2 premotor areas PMd and PMvPMd and PMv

3 cingulate motor areas3 cingulate motor areasCMAr, CMAv and CMAdCMAr, CMAv and CMAd

Secondary Motor CortexSecondary Motor Cortex

Subject of ongoing researchSubject of ongoing research In general, may be involved in In general, may be involved in

programming patterns of movements programming patterns of movements based on input from PFCbased on input from PFC

Mirror neurons Mirror neurons – in premotor cortex (also – in premotor cortex (also in posterior parietal cortex) are involved in in posterior parietal cortex) are involved in social cognition, theory of mind and may social cognition, theory of mind and may contribute to autism if dysfunctional.contribute to autism if dysfunctional.

Primary Motor CortexPrimary Motor Cortex

Precentral gyrus of the frontal lobePrecentral gyrus of the frontal lobe Major point of convergence of cortical Major point of convergence of cortical

sensorimotor signalssensorimotor signals Major point of departure of signals from cortexMajor point of departure of signals from cortex SomatotopicSomatotopic – more cortex devoted to body – more cortex devoted to body

parts which make many movementsparts which make many movements

Motor Motor homunculushomunculus

Primary Motor CortexPrimary Motor Cortex

Monkeys have two hand areas in each Monkeys have two hand areas in each hemisphere, one receives feedback from hemisphere, one receives feedback from receptors in skin.receptors in skin.

StereognosisStereognosis – recognizing by touch – requires – recognizing by touch – requires interplay of sensory and motor systemsinterplay of sensory and motor systems

Damage to primary motor cortexDamage to primary motor cortex Movement of independent body parts (e.g., 1 finger)Movement of independent body parts (e.g., 1 finger) AstereognosiaAstereognosia Speed. accuracy and force of movementSpeed. accuracy and force of movement

Other sensorimotor structures Other sensorimotor structures outside of the hierarchyoutside of the hierarchy

(sometimes called extrapyramidal systems)(sometimes called extrapyramidal systems)CerebellumCerebellumBasal gangliaBasal ganglia

both modulate and coordinate the activity of both modulate and coordinate the activity of the pyramidal systems by interacting with the pyramidal systems by interacting with different levels of the hierarchy. different levels of the hierarchy.

CerebellumCerebellum

10% of brain mass, > 50% of its neurons10% of brain mass, > 50% of its neurons Converging signals fromConverging signals from

primary and secondary motor cortexprimary and secondary motor cortex brain stem motor nuclei (descending motor signals)brain stem motor nuclei (descending motor signals) Somatosensory and vestibular systems (motor Somatosensory and vestibular systems (motor

feedback)feedback) Involved in motor learning, particularly sequences Involved in motor learning, particularly sequences

of movementof movement Damage to cerebellum – disrupts direction, force, velocity Damage to cerebellum – disrupts direction, force, velocity

and amplitude of movements; causes tremor and and amplitude of movements; causes tremor and disturbances of balance, gait, speech, eye movement and disturbances of balance, gait, speech, eye movement and motor sequence learning .motor sequence learning .

Basal Ganglia Basal Ganglia

A collection of nucleiA collection of nucleiPart of neural loops that receive cortical Part of neural loops that receive cortical

input and send output back via the input and send output back via the thalamus (cortical-basal ganglia-thalamo-thalamus (cortical-basal ganglia-thalamo-cortical loops)cortical loops)

Modulate motor output and cognitive Modulate motor output and cognitive functionsfunctions

Cognitive functions of the basal gangliaCognitive functions of the basal ganglia

Descending Motor PathwaysDescending Motor Pathways

Two dorsolateralTwo dorsolateral Corticospinal Corticospinal CorticorubrospinalCorticorubrospinal

Two ventromedialTwo ventromedial CorticospinalCorticospinal Cortico-brainstem-spinal tractCortico-brainstem-spinal tract

The corticospinal tracts are direct pathwaysThe corticospinal tracts are direct pathways

Dorsolateral Vs Ventromedial Motor Dorsolateral Vs Ventromedial Motor PathwaysPathways

VentromedialVentromedial one direct tract, one one direct tract, one

that synapses in the that synapses in the brain stembrain stem

More diffuseMore diffuse Bilateral innervationBilateral innervation Proximal musclesProximal muscles Posture and whole Posture and whole

body movementbody movement

DorsolateralDorsolateral one direct tract, one one direct tract, one

that synapses in the that synapses in the brain stembrain stem

Terminate in one Terminate in one contralateral spinal contralateral spinal segmentsegment

Distal musclesDistal muscles Limb movementsLimb movements

Experiments by Lawrence and Experiments by Lawrence and Kuypers (1968)Kuypers (1968)

Experiment 1: bilateral transection of theDorsolateral (DL) corticospinal tractResults: 1) monkeys could stand, walk and climb 2) difficulty reaching but improved over time3) could not move fingers independently of

each other or release objects from their grasp.


Experiment 2:

The same monkeys with DL corticospinal tract lesions received 1 of 2 additional lesions:

1) The other indirect DL tract was transected2) Both ventromedial (VM) tracts were

transected


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.


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.

The case of H.M.The case of H.M.

Intractable epilepsyIntractable epilepsyone generalized convulsion each weekone generalized convulsion each weekSeveral partial convulsions each daySeveral partial convulsions each day

1953 surgery: Bilateral medial temporal 1953 surgery: Bilateral medial temporal lobectomylobectomy temporal poletemporal poleamygdalaamygdalaentorhinal cortexentorhinal cortexhippocampushippocampus

Corkin et al. (1997)Corkin et al. (1997)

Corkin et al. (1997)Corkin et al. (1997)

Effects of Bilateral Medial Temporal Effects of Bilateral Medial Temporal LobectomyLobectomy

Convulsions were dramatically reducedConvulsions were dramatically reduced IQ increased from 104 to 118IQ increased from 104 to 118Short-term memory (STM) intactShort-term memory (STM) intactTemporally-graded retrograde amnesiaTemporally-graded retrograde amnesiaSevere anterograde amnesiaSevere anterograde amnesia

AmnesiaAmnesia

Retrograde Retrograde (backward-acting) – unable to (backward-acting) – unable to remember the pastremember the past

Anterograde Anterograde (forward-acting) – unable to (forward-acting) – unable to form new memoriesform new memories

While H.M. was unable to form most types While H.M. was unable to form most types of new long-term memories, his STM was of new long-term memories, his STM was intact intact

Mirror-drawing taskMirror-drawing taskH.M.’s performance H.M.’s performance

improved over 3 improved over 3 days (10 trials/day) days (10 trials/day) despite the fact despite the fact that he could not that he could not consciously consciously remember the task remember the task on days 2 and 3.on days 2 and 3.

Rotary-Pursuit TestRotary-Pursuit Test

H.M.’s performance H.M.’s performance improved over 9 improved over 9 daily practice daily practice sessions; again, sessions; again, with no recognition with no recognition of the experienceof the experience

Explicit vs Implicit MemoriesExplicit vs Implicit Memories

Explicit memoriesExplicit memories – conscious memories – conscious memories Implicit memoriesImplicit memories – unconscious memories – unconscious memories

Repetition priming tests were developed to assess Repetition priming tests were developed to assess implicit memory performance; implicit memory performance;

Incomplete pictures testIncomplete pictures test

Implications of H.M.’s amnesiaImplications of H.M.’s amnesia

Medial temporal lobes are involved in Medial temporal lobes are involved in memory formation.memory formation.

STM and LTM are dissociable – H.M. is STM and LTM are dissociable – H.M. is unable to consolidate certain kinds of unable to consolidate certain kinds of explicit memory.explicit memory.

the fact that he could form some memories the fact that he could form some memories suggests that there are multiple memory suggests that there are multiple memory systems in the brain.systems in the brain.

Medial Temporal Lobe AmnesiaMedial Temporal Lobe Amnesia Not all patients with this form of amnesia are Not all patients with this form of amnesia are

unable form new explicit long-term memories, as unable form new explicit long-term memories, as was the case with H.M.was the case with H.M.

Two kinds of explicit memory:Two kinds of explicit memory:Semantic memorySemantic memory (general information) may (general information) may

function normally while function normally while episodic memoryepisodic memory (events (events that one has experienced) does not – they are that one has experienced) does not – they are able to learn facts, but do not remember doing able to learn facts, but do not remember doing so (the episode when it occurred)so (the episode when it occurred)

Vargha-Khadem et al., (1997)Vargha-Khadem et al., (1997)

Studied three children that had bilateral Studied three children that had bilateral temporal lobe damage early in life.temporal lobe damage early in life.

Like H.M., the children could not form Like H.M., the children could not form episodic memory, however they did episodic memory, however they did acquire reasonable levels of factual acquire reasonable levels of factual knowledge and language ability in knowledge and language ability in mainstream school.mainstream school.

Effects of Cerebral Ischemia on the Effects of Cerebral Ischemia on the Hippocampus and MemoryHippocampus and Memory

R.B. suffered damage to just one part of R.B. suffered damage to just one part of the hippocampus (CA1 pyramidal cell the hippocampus (CA1 pyramidal cell layer) and developed amnesialayer) and developed amnesia

R.B.’s case suggests that hippocampal R.B.’s case suggests that hippocampal damage alone can produce amnesiadamage alone can produce amnesia

H.M.’s damage and amnesia was more H.M.’s damage and amnesia was more severe than R.B.’ssevere than R.B.’s

Object-Recognition MemoryObject-Recognition Memory Early animal models of amnesia involved implicit Early animal models of amnesia involved implicit

memory and assumed the hippocampus was memory and assumed the hippocampus was keykey

1970’s – monkeys with bilateral medial temporal 1970’s – monkeys with bilateral medial temporal lobectomies showed LTM deficits in the delayed lobectomies showed LTM deficits in the delayed nonmatching-to-sample testnonmatching-to-sample test

Like H.M., performance was normal when Like H.M., performance was normal when memory needed to be held for only a few memory needed to be held for only a few seconds (within the duration of STM)seconds (within the duration of STM)

Delayed nonmatching-to-sample taskpretend you’re the monkey

Sample stimulustouch it and get a yummy treat

10 min delay during which other sample stimuli are presented

Choice phase: pick the image that is new

Another yummy treat

Darn, no food

Testing object-recognition memoryTesting object-recognition memory

Medial temporal lobe (MTL)Medial temporal lobe (MTL)

Delayed non-match to sample resultsDelayed non-match to sample results

The Mumby BoxThe Mumby Box

Object recognition in ratsObject recognition in rats

Comparison Comparison of lesions in of lesions in

monkeys monkeys and ratsand rats

Neuroanatomy of object recognitionNeuroanatomy of object recognition

Bilateral removal of the rhinal cortex Bilateral removal of the rhinal cortex consistently results in object-recognition consistently results in object-recognition deficits.deficits.

Bilateral removal of the hippocampus Bilateral removal of the hippocampus produces moderate deficits or none at all.produces moderate deficits or none at all.

Bilateral removal of the amygdala has no Bilateral removal of the amygdala has no effect on object-recognition.effect on object-recognition.

Is the hippocampus involved in Is the hippocampus involved in object recognition memory?object recognition memory?

The Case of R.B. suggests that the lesions The Case of R.B. suggests that the lesions of the CA1 region of the hippocampus of the CA1 region of the hippocampus (due to ischemia) can produce severe (due to ischemia) can produce severe memory deficitsmemory deficits

Ischemia in animal models also produces Ischemia in animal models also produces deficits in object recognitiondeficits in object recognition

Yet deficits in object recognition are only Yet deficits in object recognition are only moderate to non-existent in other animal moderate to non-existent in other animal lesion modelslesion models

Why?Why?

Mumby et al. (1996)Mumby et al. (1996)

Bilateral hippocampectomy actually blocks Bilateral hippocampectomy actually blocks the damage produced by ischemia!the damage produced by ischemia!

Explanation:Explanation: Ischemia causes hippocampal neurons to Ischemia causes hippocampal neurons to

release glutamate, which produces release glutamate, which produces damage outside of the hippocampus damage outside of the hippocampus (particularly in rhinal cortex), although (particularly in rhinal cortex), although standard histological techniques do not standard histological techniques do not show the damage follow-up functional show the damage follow-up functional imaging studies have confirmed the imaging studies have confirmed the dysfunction.dysfunction.

The HippocampusThe Hippocampus

Rhinal cortex plays an important role in Rhinal cortex plays an important role in object recognition.object recognition.

Hippocampus plays a key role in memory Hippocampus plays a key role in memory for spatial location.for spatial location.Hippocampectomy produces deficits on Hippocampectomy produces deficits on

Morris maze and radial arm maze Morris maze and radial arm maze (Chapter 5)(Chapter 5)

Many hippocampal cells are place cells – Many hippocampal cells are place cells – responding when a subject is in a responding when a subject is in a particular placeparticular place

Theories of Hippocampal FunctionTheories of Hippocampal Function

O’Keefe & Nadel (1978) Cognitive map theory – O’Keefe & Nadel (1978) Cognitive map theory – constructs and stores allocentric maps of the constructs and stores allocentric maps of the worldworld

Rudy & Sutherland (1992) Configural Rudy & Sutherland (1992) Configural association theory – involved in retaining the association theory – involved in retaining the behavioral significance of combinations of behavioral significance of combinations of stimulistimuli

Brown & Aggleton (1999) is involved in Brown & Aggleton (1999) is involved in recognizing the spatial arrangements of objectsrecognizing the spatial arrangements of objects

Synaptic Mechanisms of Learning Synaptic Mechanisms of Learning and Memoryand Memory

What is happening within the brain What is happening within the brain structures involved in memory?structures involved in memory?

Hebb – changes in synaptic efficiency are Hebb – changes in synaptic efficiency are the basis of LTMthe basis of LTM

Long-term potentiation (LTP) – synapses Long-term potentiation (LTP) – synapses are effectively made stronger by repeated are effectively made stronger by repeated stimulationstimulation

Long Term Potentiation (LTP)

C a 2+

N a A P -5

H A -966

M K -801M g 2+

+

K+

M g 2+

G lu tam ate

Zn 2+

G lyc ine

P o lyam ine

P C P

N M D A

D-C yclose rine

Cross-section of the NMDA receptor complex

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Sensorimotor systems Learning, memory & amnesia Chapters 8 and 11