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POWERPOINT PRESENTATION FOR BIOPSYCHOLOGY, 9TH EDITION BY JOHN P.J. PINEL P R E PA R E D B Y J E F F R E Y W. G R I M M WESTERN WASHINGTON UNIVERSITY COPYRIGHT © 2014 PEARSON EDUCATION, INC. ALL RIGHTS RESERVED. This multimedia product and its contents are protected under copyright law. The following are prohibited by law: • any public performance or display, including transmission of any image over a network; • preparation of any derivative work, including the extraction, in whole or in part, of any images; • any rental, lease, or lending of the program. Chapter 8 The Sensorimotor System How You Move Copyright © 2014 Pearson Education, Inc. All rights reserved. Learning Objectives LO1: List and discuss 3 principles of sensorimotor function. LO2: Describe 2 major areas of sensorimotor association cortex and evidence of their functions. LO3: List the current areas of secondary motor cortex. LO4: Discuss mirror neurons. LO5: Describe the organization of primary motor cortex and the current view of its function. LO6: Discuss the functions of the cerebellum and basal ganglia. LO7: List and explain the 4 descending motor pathways. LO8: Summarize the classic study of Lawrence and Kuypers. LO9: Describe the neural circuits that control muscles. LO10: Explain the stretch reflex, withdrawal reflex, and walking reflex. LO11: Discuss central sensorimotor programs and the principles of sensorimotor learning. Copyright © 2014 Pearson Education, Inc. All rights reserved. Three Principles of Sensorimotor Function Hierarchical Organization Association cortex at the highest level, muscles at the lowest Parallel structure: signals flow between levels over multiple paths Motor output is guided by sensory input. Learning changes the nature and locus of sensorimotor control. E.g., conscious to automatic Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.1 A general model of the sensorimotor system. Notice its hierarchical structure, functional segregation, parallel descending pathways, and feedback circuits. Copyright © 2014 Pearson Education, Inc. All rights reserved. Sensorimotor Association Cortex Posterior Parietal Association Cortex Dorsolateral Prefrontal Association Cortex Each is composed of several different areas with different functions. Some disagreement exists regarding how to divide the areas up. Copyright © 2014 Pearson Education, Inc. All rights reserved. Posterior Parietal Association Cortex Integrates Information about: Body part location External objects Receives Visual, Auditory, and Somatosensory Information Outputs to Motor Cortex Including dorsolateral prefrontal association cortex, secondary motor cortex, and frontal eye field Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.2 The major cortical input and output pathways of the posterior parietal association cortex. Shown are the lateral surface of the left hemisphere and the medial surface of the right hemisphere. Copyright © 2014 Pearson Education, Inc. All rights reserved. Damage to the Posterior Parietal Cortex Apraxia: disorder of voluntary movement; problem only evident when instructed to perform an action; usually a consequence of damage to the area on the left Contralateral neglect: inability to respond to stimuli contralateral to the side of the lesion; usually seen with large lesions on the right Copyright © 2014 Pearson Education, Inc. All rights reserved. Dorsolateral Prefrontal Association Cortex Input from Posterior Parietal Cortex Output to Secondary Motor Cortex, Primary Motor Cortex, and Frontal Eye Field The dorsolateral prefrontal association cortex evaluates external stimuli and initiates voluntary reactions; it is supported by neuronal responses. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.3 The major cortical input and output pathways of the dorsolateral prefrontal association cortex. Shown are the lateral surface of the left hemisphere and the medial surface of the right hemisphere. Copyright © 2014 Pearson Education, Inc. All rights reserved. Secondary Motor Cortex Input Mainly from Association Cortex Output Mainly to Primary Motor Cortex Copyright © 2014 Pearson Education, Inc. All rights reserved. Identifying the Areas of Secondary Motor Cortex There are at least eight different areas. Three Supplementary Motor Areas Two Premotor Areas SMA and preSMA, and supplementary eye field Dorsal and ventral Three Cingulate Motor Areas Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.4 Four areas of secondary motor cortex—the supplementary motor area, the premotor cortex, and two cingulate motor areas—and their output to the primary motor cortex. Shown are the lateral surface of the left hemisphere and the medial surface of the right hemisphere. Copyright © 2014 Pearson Education, Inc. All rights reserved. Identifying the Areas of Secondary Motor Cortex (Con’t) The secondary motor cortex may be involved in programming movements in response to input from the dorsolateral prefrontal cortex. Active during imagining or planning of movements Copyright © 2014 Pearson Education, Inc. All rights reserved. Mirror Neurons Mirror neurons are active when performing an action or watching another perform the same action. In monkey studies, mirror neurons fired while: Grasping or watching another grasp a particular object but not other objects Grasping or watching another grasp an object for a specific purpose but not for another purpose Mirror neurons are a possible neural basis of social cognition (knowledge of others’ mental processes— e.g., intentions). Likely to Be Found in Humans Indirect evidence from functional brain-imaging studies Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.5 Responses of a mirror neuron of a monkey. Copyright © 2014 Pearson Education, Inc. All rights reserved. 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 Copyright © 2014 Pearson Education, Inc. All rights reserved. Conventional View of Primary Motor Cortex Function Somatotopic: more cortex devoted to body parts that make complex movements Motor homunculus Until recently, each neuron was thought to encode the direction of movement. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.6 The motor homunculus: the somatotopic map of the human primary motor cortex. Stimulation of sites in the primary motor cortex elicits simple movements in the indicated parts of the body. (Based on Penfield & Rasmussen, 1950.) Copyright © 2014 Pearson Education, Inc. All rights reserved. Current View of Primary Motor Cortex Function Regions of primary motor cortex support initiation of species-typical movements. Neurons direct to target of movement, rather than simply a pre-coded direction. Copyright © 2014 Pearson Education, Inc. All rights reserved. Effects of Primary Motor Cortex Lesions Small lesions often have minimal effects. Large lesions may disrupt a patient’s ability to move one body part independently of others. Large lesions may also produce stereognosia. Deficit in stereognosis (ability to identify an object by touch) Copyright © 2014 Pearson Education, Inc. All rights reserved. Cerebellum and Basal Ganglia Interact with Different Levels of the Sensorimotor Hierarchy Coordinate and Modulate May Permit Maintenance of Visually Guided Responses Despite Cortical Damage Copyright © 2014 Pearson Education, Inc. All rights reserved. Cerebellum 10 Percent of Brain Mass, but More than 50 Percent of Its Neurons Input from Primary and Secondary Motor Cortexes Input from Brainstem Motor Nuclei Feedback from Motor Responses Involved in Timing, Fine-Tuning, and Motor Learning May Also Do the Same for Cognitive Responses Copyright © 2014 Pearson Education, Inc. All rights reserved. Basal Ganglia A Heterogeneous Collection of Interconnected Nuclei Part of Neural Loops that Receive Cortical Input and Send Output Back via the Thalamus Modulate Motor Output and Cognitive Functions, Including Learning Copyright © 2014 Pearson Education, Inc. All rights reserved. Descending Motor Pathways Two Dorsolateral Two Ventromedial Corticospinal Corticorubrospinal Corticospinal Cortico-brainstem-spinal tract Both corticospinal tracts are direct. Copyright © 2014 Pearson Education, Inc. All rights reserved. Dorsolateral Tracts Most dorsolateral tracts synapse on interneurons of spinal gray matter. Corticospinal: descend through the medullary pyramids, then decussate Betz cells: synapse on motor neurons projecting to leg muscles Control of wrist, hands, fingers, toes Corticorubrospinal: synapse at red nucleus and cross before the medulla Some control muscles of the face Distal muscles of arms and legs Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.7 The two divisions of the dorsolateral motor pathway: the dorsolateral corticospinal tract and the dorsolateral corticorubrospinal tract. The projections from only one hemisphere are shown. Copyright © 2014 Pearson Education, Inc. All rights reserved. Ventromedial Tracts Corticospinal Descends ipsilaterally Axons branch and innervate interneuron circuits bilaterally in multiple spinal segments. Cortico-Brainstem-Spinal Interacts with various brainstem structures and descends bilaterally, carrying information from both hemispheres Synapses on interneurons of multiple spinal segments controlling proximal trunk and limb muscles Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.8 The two divisions of the ventromedial motor pathway: the ventromedial corticospinal tract and the ventromedial cortico-brainstem-spinal tract. The projections from only one hemisphere are shown. Copyright © 2014 Pearson Education, Inc. All rights reserved. Comparison of the Two Dorsolateral Motor Pathways and the Two Ventromedial Motor Pathways Dorsolateral Ventromedial One direct tract, one that synapses in the brain stem Terminate in one contralateral spinal segment Distal muscles Limb movements One direct tract, one that synapses in the brain stem More diffuse Bilateral innervation Proximal muscles Posture and whole body movement Copyright © 2014 Pearson Education, Inc. All rights reserved. Sensorimotor Spinal Circuits Motor circuits of the spinal cord show considerable complexity. Independent of signals from the brain Copyright © 2014 Pearson Education, Inc. All rights reserved. Muscles Motor units: a motor neuron plus muscle fibers; all fibers contract when the motor neuron fires. Number of fibers per unit varies; fine control, fewer fibers/neuron Muscle: muscle fibers bound together by a tendon Copyright © 2014 Pearson Education, Inc. All rights reserved. Muscles (Con’t) Acetylcholine released by motor neurons at the neuromuscular junction causes contraction. Motor pool: all motor neurons innervating the fibers of a single muscle Fast muscle fibers fatigue quickly. Slow muscle fibers are capable of sustained contraction due to vascularization. Muscles are a mix of slow and fast fibers. Copyright © 2014 Pearson Education, Inc. All rights reserved. Muscles (Con’t) Flexors bend or flex a joint. Extensors straighten or extend. Synergistic muscles: any two muscles whose contraction produces the same movement Antagonistic muscles: any two muscles that act in opposition Copyright © 2014 Pearson Education, Inc. All rights reserved. Receptor Organs of Tendons and Muscles Golgi Tendon Organs Embedded in tendons Tendons connect muscle to bone. Detect muscle tension Copyright © 2014 Pearson Education, Inc. All rights reserved. Receptor Organs of Tendons and Muscles (Con’t) Muscle Spindles Embedded in muscle tissue Detect changes in muscle length Intrafusal muscle within each muscle spindle is innervated by its own intrafusal motor neuron. Keeps tension on the middle, stretch-sensitive portion of the muscle spindle to keep it responsive to changes in the length of the extrafusal muscle Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.11 The muscle-spindle feedback circuit. There are many muscle spindles in each muscle; for clarity, only one muchenlarged muscle spindle is Illustrated here. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.12 The function of the intrafusal motor neurons. Copyright © 2014 Pearson Education, Inc. All rights reserved. Reflexes Stretch reflex: monosynaptic; serves to maintain limb stability E.g., The patellar tendon reflex is monosynaptic. Withdrawal reflex is NOT monosynaptic. Reciprocal innervation: antagonistic muscles interact so that movements are smooth; flexors are excited while extensors are inhibited, etc. Recurrent collateral inhibition: feedback loop through Renshaw cells that gives muscle fiber a rest after every contraction Walking: a complex reflex in some animals Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.13 The elicitation of a stretch reflex. All of the muscle spindles in a muscle are activated during a stretch reflex, but only a single muscle spindle is depicted here. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.16 The excitatory and inhibitory signals that directly influence the activity of a motor neuron. Copyright © 2014 Pearson Education, Inc. All rights reserved. Central Sensorimotor Programs Perhaps all but the highest levels of the sensorimotor system have patterns of activity programmed into them, and complex movements are produced by activating these programs. Cerebellum and basal ganglia then serve to coordinate the various programs. Copyright © 2014 Pearson Education, Inc. All rights reserved. Central Sensorimotor Programs Are Capable of Motor Equivalence A given movement can be accomplished various ways, using different muscles. Central sensorimotor programs must be stored at a level higher than the muscle (as different muscles can do the same task). Sensorimotor programs may be stored in secondary motor cortex. Copyright © 2014 Pearson Education, Inc. All rights reserved. Sensory Information that Controls Central Sensorimotor Programs Is Not Necessarily Conscious There is evidence that patients can respond to visual stimuli of which they have no conscious awareness. There is also evidence that patients can not effectively interact with objects that they consciously perceive. Ebbinghaus illusion: conscious perception of disk size differs from motor response. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.17 The Ebbinghaus illusion. Notice that the central disk on the left appears larger than the one on the right. Haffenden and Goodale (1998) found that when volunteers reached out to pick up either of the central disks, the position of their fingers as they approached the disks indicated that their responses were being controlled by the actual sizes of the disks, not their consciously perceived sizes. Copyright © 2014 Pearson Education, Inc. All rights reserved. The Development of Central Sensorimotor Programs Central sensorimotor programs may be hierarchically organized and capable of using sensory feedback without direct control at higher levels. Programs for many species-specific behaviors are established without practice. Fentress (1973): mice without forelimbs still make coordinated grooming motions. Copyright © 2014 Pearson Education, Inc. All rights reserved. The Development of Central Sensorimotor Programs (Con’t) Practice can also generate and modify programs. Response Chunking Practice combines the central programs controlling individual response. Shifting Control to Lower Levels Frees up higher levels to do more complex tasks Permits greater speed Copyright © 2014 Pearson Education, Inc. All rights reserved. Functional Brain Imaging of Sensorimotor Learning Functional brain-imaging studies in humans have generally supported the findings from more invasive studies of non-human primates. Copyright © 2014 Pearson Education, Inc. All rights reserved. FIGURE 8.18 The activity recorded by PET scans during the performance of newly learned and well-practiced sequences of finger movements. (Based on Jenkins et al., 1994.) Copyright © 2014 Pearson Education, Inc. All rights reserved.