NEUR3101_Lec5_CorticalControl_FvW_Part1-2_1perpage.pdf

Cortical control of movement Part 1: Mapping the primary motor cortex Dr. Frederic von Wegner WARN...

Cortical control of movement Part 1: Mapping the primary motor cortex Dr. Frederic von Wegner WARNING  This material has been reproduced and communicated to you by or on behalf of the University of New South Wales in accordance with section 113P of the Copyright Act 1968 (Act).  The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act.  Do not remove this notice Motor pathways and networks pathway view: serial connection of two neurons: a) upper motor neuron (brain) b) lower motor neuron (spinal cord) corticospinal tract pyramidal tract (brainstem decussation) Guyton&Hall, Textbook of Medical Physiology Duus’ Topical Diagnosis in Neurology Motor pathways and networks pathway view: serial connection of two neurons: a) upper motor neuron (brain) b) lower motor neuron (spinal cord) corticospinal tract pyramidal tract (brainstem decussation) Guyton&Hall, Textbook of Medical Physiology Duus’ Topical Diagnosis in Neurology Motor pathways and networks network view, there are many loops: a) cortico-cortical b) cortex-basal ganglia c) cortico-thalamic d) cortex-cerebellar e) cortex-brainstem... Guyton&Hall, Textbook of Medical Physiology Duus’ Topical Diagnosis in Neurology Focus on voluntary movement Common structures Grillner, Physiol Rev, 2020 Current Principles of Motor Control  Do you need a motor cortex to move? Answer: no Ebbesen, Nat Rev Neurosci 2017, Motor cortex, to act or not to act?  The map perspective  historically, many lesion studies (trauma, armed conflicts)  postmortal examinations of focal lesions  early brain surgery Lüders, Textbook of Epilepsy Surgery  The map perspective  historically, many lesion studies (trauma, armed conflicts)  postmortal examinations of focal lesions  early brain surgery  cortex localisation  movement of a body region  concept: cortex = map Lüders, Textbook of Epilepsy Surgery  Experimental evidence  Intraoperative brain stimulation (identify functionally important regions)  Presurgical diagnostics (epilepsy surgery): implantation of intracranial electrodes, option to record and stimulate electrode contacts at defined anatomical sites intracranial electrode Multiple contacts: 1…8 Lüders, Textbook of Epilepsy Surgery  Cortex mapping by electrical stimulation Penfield, Brain, 1937  map-like activation characteristics  Cortex mapping by electrical stimulation lateral Other experiments:  map-like inhibition ventral characteristics medial Penfield (from Ebbesen, Nat Rev Neurosci, 2017  Motor cortices Guyton&Hall, Textbook of Medical Physiology  Somatotopic map of the primary motor cortex Duus’ Topical Diagnosis in Neurology Guyton&Hall, Textbook of Medical Physiology  Somatotopic map of the primary motor cortex Somatotopic mapping: each body region has its own representation in the brain Neighbouring body parts are neighbours in the brain The representation is distorted: body regions with higher innervation density occupy larger cortex areas https://en.wikipedia.org/wiki/Cortical_homunculus  Cortical control of movement Part 2: Motor cortices – an overview Dr. Frederic von Wegner WARNING  This material has been reproduced and communicated to you by or on behalf of the University of New South Wales in accordance with section 113P of the Copyright Act 1968 (Act).  The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act.  Do not remove this notice  Primary motor cortex (M1)  somatotopic organization (brain has a body map)  encodes activation of (single muscles and) groups of muscles Guyton&Hall, Textbook of Medical Physiology  Primary motor cortex (M1)  somatotopic organization  encodes activation of (single muscles and) groups of muscles  encodes force production in these muscles, but also inhibits others (task dependent) Kandel, Principles of Neural Science  Primary motor cortex (M1)  somatotopic organization  encodes activation of (single muscles and) groups of muscles  encodes force production in these muscles, but also inhibits others  encodes direction of movement Each tick = 1 action potential Kandel, Principles of Neural Science  Primary motor cortex (M1)  somatotopic organization  encodes activation of (single muscles and) groups of muscles  encodes force production in these muscles, but also inhibits others  encodes direction of movement Kandel, Principles of Neural Science  Primary motor cortex (M1)  somatotopic organization  encodes activation of (single muscles and) groups of muscles  encodes force production in these muscles, but also inhibits others  encodes direction of movement  the population vector: characterizes the directional preference of a large group of neurons Each ray: 1 neuron, length=discharge rate, angle = preferred movement direction Blue vector: vector sum of discharge rates Dashed vector: actual arm movement Conclusion: vector sums of neuronal activities predict the actual movement Kandel, Principles of Neural Science  Directional tuning of M1 neurons  somatotopic organization  encodes activation of (single muscles and) no load external load groups of muscles  encodes force production in these muscles, but also inhibits others  encodes direction of movement  the population vector (many neurons)  combining direction and force: the brain adjusts the activity of all motor cortex neurons to counteract an opposing external force to reach a target (error correction) Kandel, Principles of Neural Science  Premotor cortex / area (PM)  extended region frontal to the primary motor cortex, lateral of the SMA  encoding of complex action sequences,  coordination with cerebellum and basal ganglia  connection with visual and afferent areas  hand-related activity: grasp, manipulation  coordinated eye-head movements (frontal eye field)  direct connection to the spinal cord > isolated M1 lesions recover > isolated PM lesions recover > combined lesions much less Guyton&Hall, Textbook of Medical Physiology  Premotor cortex / area (PM)  extended region frontal to the primary motor cortex, lateral of the SMA  encoding of complex action sequences,  coordination with cerebellum and basal ganglia  connection with visual and afferent areas  hand-related activity: grasp, manipulation  coordinated eye-head movements (frontal eye field)  direct connection to the spinal cord > isolated M1 lesions recover > isolated PM lesions recover > combined lesions much less  Supplementary motor area (SMA)  frontal to M1  near the midline, medial to PM  encodes bilateral movements and movements of all limbs  encodes multi-muscle, multi-joint movements and sequences  motor sequence rehearsing (motor imagery) Guyton&Hall, Textbook of Medical Physiology  Supplementary motor area (SMA)  frontal to M1  near the midline, medial to PM  encodes bilateral movements and movements of all limbs  encodes multi-muscle, multi-joint movements and sequences  motor sequence rehearsing (motor imagery)  Prefrontal cortex  Prefrontal cortex makes complex movement plans: sequences of bilateral, multi-joint, multi-muscle movement patterns  lying down/standing up, cycling  can include articulation (sounds, speech)  connection to motivational and emotional brain regions  Uncontrolled activity leads to complex, potentially dangerous movements (jerking, jumping)  Complex prefrontal activity (epileptic)  Prefrontal cortex makes complex movement plans: sequences of bilateral, multi-joint, multi-muscle movement patterns  lying down/standing up, cycling  can include articulation (sounds, speech)  connection to motivational and emotional brain regions  Uncontrolled activity leads to complex, potentially dangerous movements (jerking, jumping)  Executive functions (prefrontal cortex) Luria, Higher Cortical Functions in Man  Executive functions (prefrontal cortex) repetitive task performance = perseveration characteristic symptom of prefrontal cortical lesions Luria, Higher Cortical Functions in Man  Functional movement disorders  emotions affect movement planning and execution  very frequent disorders  often: tremor, myoclonic tics/jerks, dystonia,  non-epileptic seizures  in elderly: phobic gait disorder  neural correlates in fMRI: stronger connectivity between motor cortices and amygdala (emotional processing, fear) Baizabal-Carvallo, Neurobiol of Disease, 2019  Summary  there is a system of motor cortices  we discussed: primary motor cortex (M1), premotor areas (PM) and the supplementary motor area (SMA)  they are connected to all other motor systems (basal ganglia, brainstem, cerebellum...)  M1 encodes: activation of single muscles/small muscle groups, force, orientation  PM encodes: sequential and multi-muscle activation, hand-related coordination  SMA encodes: bilateral, sequential and multi-joint movements  the fundamental connection volition – motor initiation remains unclear