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Chapter 8

PSYC 211 Chapter 8

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PSYC 211
Yogita Chudasama

Chapter 8: Control of Movement –Psych 211 Behavioral Neuroscience Case Study: Mr. J:  Had a severe stroke and had damage to left parietal lobe  Had severe Apraxia: Apraxia is a disorder of the brain and nervous system in which a person is unable to perform tasks or movements when asked, even though: • The request or command is understood • They are willing to perform the task • The muscles needed to perform the task work properly • The task may have already been learned  Was not able to wave hello when asked to do so, but could do it automatically when meeting someone since it was something learned. He couldn’t make even a simple movement out of context.  Left parietal lobe is involved in the control of movements- especially sequences of movement-that are not dictated by the context.  Ultimate function of the Nervous System: Control of Behavior – Making our bodies move is most important. CONTROL OF MOVEMENT • Movements can be initiated by several reasons, for ex.: 1. Rapid stretch of muscle triggers the monosynaptic stretch reflex 2. A stumble triggers righting reflexes 3. Rapid approach of an object toward the face causes a startle response, a complex reflex consisting of movements of several muscle groups. 4. Presence of food causes eating 5. Sight of a loved one evokes a hug and a kiss  Because there is no single cause of behavior, we can’t find a single starting point in our search for the neural mechanisms that control movement. • The brain and spinal cord include several different, motor systems, each of which can simultaneously control particular kinds of movements. ORGANIZATION OF THE MOTOR CORTEX: • The primary motor cortex lies on the precentral gyrus, just rostral to the central sulcus. • Studies show that activation of neurons in particular parts of primary motor cortex causes movements of particular parts of the body. • The primary motor cortex shows somatotopic organization • Somatotopic Organization: A topographically organized mapping of parts of the body that are represented in a particular region of the brain.  fig 8.9  NOTE: A disproportionate amount of cortical area is devoted to movements of the fingers and the muscles used for speech. • Primary cortex is organized in terms of particular movements of particular parts of the body.  Each movement may be accomplished by the contraction of several muscles.  Examples: When the arm is extended in a particular direction, many muscles in the shoulder, upper arm, and forearm must contract.  This fact means that complex neural circuitry is located between individual neurons in the primary motor cortex and the motor neurons in the spinal cord that cause motor units to contract.  The commands for movements initiated in the motor cortex are assisted and modified-most notable by basal ganglia and cerebellum. • Study Graziano and Aflalo:  Found that although brief stimulation of particular regions of the primary motor cortex of monkeys caused brief movements of various parts of the body, prolonged stimulation produced much more complex movements .  EX: Stimulation of one region caused the hand to close and then approach the mouth and then the mouth to open. Stimulation of another area caused the face to squint, the head to turn quickly to one side, and the arms to fling up, as if to protect the face from something that was going to hit it.  Stimulation of different zones of the motor cortex caused different categories of action. Map of these categories was consistent from animal to animal. • Principal cortical input to the primary motor cortex is the frontal association cortex, located rostral to it. • Two regions immediately adjacent to the primary motor cortex- the supplementary motor area and the premotor cortex- are especially important in the control of movement.  Both regions receive sensory info from the parietal and temporal lobes  Both send efferent axons to the primary motor cortex.  Supplementary Motor Area (SMA): Located on the medial surface of the brain, just rostral to the primary motor cortex.  A region of motor association cortex of the dorsal and dorsomedial frontal lobe.  Premotor Cortex: A region of motor association cortex, located primarily on the lateral frontal lobe surface, also just rostral to the primary motor cortex. CORTICAL CONTROL OF MOVEMENT: THE DESCENDING PATHWAYS: • Neurons in PMC ( primary motor cortex), control movement by 2 groups of descending tracts: 1. Lateral Group: The corticospinal tract, the corticobulbar tract, and the rubrospinal tract. o Primarily involved in control of independent limb movements, particularly movements of the hands and fingers. o Independent limb movements means that the right and left limbs make different movements, or one limb moves while the other remains still. o These movements contrast with coordinated limb movements, such as those involved in locomotion. 2. Ventromedial Group: The vestibulospinal tract, the tectospinal tract, the reticulospinal tract, and the ventral corticospinal tract. Named for their location in the white matter of the spinal cord. o These tracts control more autonomic movements o Gross movements of the muscles of the trunk and coordinated trunk and limb movements involved in posture and locomotion. • Lateral Group: 1. Corticospinal Tract: Consists of axons of that originate in the motor cortex and terminate in the ventral grey matter of the spinal cord.  Largest concentration of cell bodies responsible for these axons is located in the Primary Motor Cortex, but neurons in the parietal and temporal lobes also send axons through the corticospinal pathway.  The axons leave the cortex and travel through subcortical white matter to the ventral midbrain, where they enter cerebral penduncles.  They leave the penduncles in the medulla and form the pyramidal tracts. 2. Pyramidal Tracts: The portion of the corticospinal tract on the ventral border of the medulla.  At the level of the caudal medulla, most of the fibers decussate (cross over) and descend through the contralateral spinal cord, forming the lateral corticospinal tract. 3. Lateral corticospinal tract: The system of axons that originates in the motor cortex and terminates in the contralateral ventral gray matter of the spinal cord; controls movements of the distal limbs.  The rest of the fibers descend through the ipsilateral spinal cord, forming the central corticospinal tract. 4. Ventral Corticospinal tract: The system of axons that originates in the motor cortex and terminates in the ipsilateral ventral gray matter of the spinal cord; controlz movements of the upper legs and trunks.  Because of its location and function, it’s actually part of the ventromedial group. • Most axons in the lateral corticospinal tract originate in the regions of the Primary motor cortex and supplementary motor area that control the distal parts of the brain:  The arms, hands, and fingers and the lower leg, feet, and toes.  They form synpases, directly or via interneurons, with motor neurons in the gray matter of the spinal cord-in the lateral part of the ventral horn.  The motor neurons control muscles of the distal limbs, including those that move the arms, hands, and fingers. • Axons in ventral corticospinal tract originate in the upper leg and trunk regions of the primary motor cortex  The descend to the appropriate region of the spinal cord and divide, sending terminal buttons into both sides of the grey matter  They control motor neurons that move the muscles of the upper legs and trunk • Corticospinal pathway controls hand and fingers movements and is indispensable for moving the fingers independently when reaching and manipulating.  Postural adjustments of the trunk and use of the limbs for reaching and locomotion are unaffected; therefore these types of movements are controlled by other systems.  EX: Monkeys having trouble releasing their grasp when picking up objects, but having no trouble doing so when climbing walls of cage. Can conclude that the same behavior (opening the hand) is controlled by different brain mechanisms in diff. contexts. • 2ndlateral group of descending pathways: Corticobulbar Tract:  Projects to the medulla  Controls movement of the face, neck, tongue, and parts of the extraocular eye muscles. • 3rdlateral group: Rubrospinal Tract:  The system of axons that travels from the red nucleus to the spinal cord; controls independent limb movement. nd • 2 set of pathways originating in brain stem: Ventromedial group: o Vestibulospinal tracts: A bundle of axons that travels from the vestibular nuclei to the grey matter of the spinal cord; controls postural movements in response to information from the vestibular system o Tectospinal Tracts: A bundle of axons that travels from the tectum to the spinal cord; coordinates head and trunk movements with eye movements. o Reticulospinal Tracts: A bundle of axons that travels from the reticular formation to the grey matter of the spinal cord; controls the muscles responsible for postural movement. PLANNING AND INITIATING MOVEMENTS: ROLE OF THE MOTOR ASSOCIATON CORTEX: • Supplementary Motor Area and the Premotor cortex are involved in the planning of movements  they execute these plans through their connections with the primary motor cortex  Functional-imaging shows that when people execute sequences of movements-or even imagine them-these regions become activated  Evidence indicates that the motor association cortex is also involved in imitating the actions of other people (an ability that makes it possible to learn new behaviors from them) and even in understanding the functions of other people’s behaviors. • Supplememtary motor area and premotor cortex receive info from association areas of the parietal and temporal cortex:  Visual association cortex organized in two streams: (Ventral &Dorsal) 1. Ventral: terminates in the inferior temporal cortex, is involves in perceiving and recognizing particular objects- the “what” of visual perception. 2. Dorsal: terminates in the posterior parietal lobe, is involved in perception of location- the “where” of visual perception.  In addition, parietal lobes is also involved in organizing visually guided movements-the “how” of visual perception.  Also receives info about spatial location from the somatosensory, vestibular, and auditory systems and integrates this info with visual info.  Thus, the regions of the frontal cortex that are involved in planning movements, receive the info they need about what is happening from the temporal and parietal lobes.  Because the parietal lobes contain special info, the pathway from them to the frontal lobes is especially important in controlling both locomotion and arm and hand movements.  Meaningful locomotion requires us to know where we are , and meaningful movements of our arms and hands require us to know where objects are located in space. SUPPLEMENTARY MOTOR AREA: • Involved in learning and performing behaviors that consist of sequences of movements.  A nearby region area seems to be involved in initiating spontaneous movements. BEHAVIORAL SEQUENCES.  Damage to this region disrupts the ability to execute well learned sequences of responses in which the performance of one response serves as the signal that the next response must be made.  Chen et al. found that lesions of the supplementary motor area severely impaired monkeys’ ability to perform a simple sequence of two responses: pushing a lever in and then turning it to the left, receiving a peanut after each response.  Single unit study came to similar conclusion: o Monkeys were trained to perform a memorized series of responses, pressing each of three buttons in a specific sequence. o While monkeys were performing task, more than half of the neurons in the supplementary motor area became activated. o However, when the sequence was cued by visual stimuli-the monkeys simply had to press the button that was illuminated-these neurons showed little activity.  Shima and Tanji (2000) taught monkeys 6 sequences of three motor responses: o For ex, one of the sequences was push, then pull, then turn. o They recorded from neurons in the supplementary motor area found neurons whose activities appeared to encode elements of these sequences. o For ex, some neurons responded just before a particular sequence of three movements occurred; some neurons responded between two particular responses, and some neurons responded as the monkey was preparing to make the last response of the sequence. o Presumably, these neurons were members of circuits that encoded the info necessary to perform the six sequences.  Shima &Tanji (1998) temporarily inactivated the supplementary motor area in monkeys with injections of muscimol, a drug that stimulates GABA receptors and thus inhibits neural activity. o They found that after inactivation of this region, monkeys could still reach for objects or make particular movements in response to visual cues but could no longer make a sequence of three movements they had previously learned.  Funtional-imaging study by Hikosaka et al. : o Observed increased activity in the posterior SMA during performance of a learned sequence of button presses.  Gerloff et al. taught people to make a sequence of 16 finger presses on a piano: o When the researcherts disrupted the activity of the SMA with transcranial magnetic stimulation, the performance of the sequence was disrupted. o However, disruption was not immediate: The subjects continued the sequence for approx. 1 sec. and then stopped, saying they “didn’t know anymore which series of keys to press next” o Apparently, SMA is involved in planning the elements yet to come in sequences of movements o Actual execution of these movements seems to be controlled by the primary motor cortex.  Pre-SMA: o A region just anterior to the supplementary motor area o Appears to be involved in control of spontaneous movements o Has long been known that although electrical stimulation of the motor cortex causes movements, it does not produce the desire to move o Movement is perceived as automatic and involuntary. o In contrast, electrical stimulation of the medial surface of the frontal lobes ( including SMA and pre-SMA) often provokes the urge to make a movement or at least the anticipation that a movement is about to occur. o Functioning-imaging study by Lau et al. :  Found that the pre-SMA became active just before people performed spontaneous movements.  Experimenters asked subjects to make a finger movement from time to time, whenever they felt like doing so.  The subjects watched a red light that moved around a clock face at about 2,5 sec per revolution.  They were asked to pay attention to the instant when they decided to make the movement and report the position of the red dot at that time.  The decision appeared to occur 0.2 sec. before the movement began, however fMRI showed that the activity of the pre-SMA actually began to increaser 2-3 sec. earlier than that.  This suggests that the neural activity responsible for the decision to move begins before a person is even aware of making that decision.  The most important input to the SMA comes from the parietal lobes: o Sirigu et al. (2004) used a task similar to the one in the study by Lau et al. to investigate decision making in people with lesions of the parietal cortex. o They found that people with parietal lesions could accurately report when they started the movements, but they were not aware of an intention to move prior to making the movement. o These results suggest that info received from the parietal lobes permits the pre-SMA to detect that a decision to move has been made. o Location of the neural circuits actually responsible for the decision are not known, although Sirigu and her colleagues note that lesions of the prefrontal cortex (even more anterior than the pre-SMA) disrupt people’s plans for voluntary action. o People with prefrontal lesions will react to events but show deficits in initiating behavior so perhaps the prefrontal cortex is an important source of these decisions. PREMOTOR CORTEX: • Involved in imitating responses of other people and in understanding and predicting these actions • Involved in learning and executing complex movements that are guided by sensory information. • Studies suggest that the premotor cortex is involved in using arbitrary stimuli to indicate what movement should be made  EX: Reaching for an object that we see in a particular location involves nonarbitrary spatial information  That is, the visual information provided by the location of the object specifies just where we should target our reaching movement. • We also have ability to learn to make movements based on arbitrary information- information that is not directly related to the movement that it signals.  EX: A person can point to a particular object when someone says its name, or a dancer can make a particular movement when asked to do so by a choreographer.  Diff. languages use diff. sounds to indicate the names of objects, and diff. choreographers could invent diff. names for movements used in their dancers.  The association between these stimuli and the movements they designate are arbitrary and must be learned. • Kurata &Hoffman (1994) trained monkeys to move their hands toward the right or left in response to either spatial or a non- spatial signal:  The spatial signal required a monkey to move in the direction indicated by signal lights located on the right or left of the hand.  The non-spatial signal consisted of a pair of lights, one red and one green, located in the middle of the display. o Red light signaled a movement to the left, and green light signaled a movement to the right. o The investigators temporarily inactivated the premotor cortex with injections of muscimol. o When this region was inactivated, the monkeys could still move their hands towards a signal light located to the left or right (a non-arbitrary signal), but they could no longer make the appropriate movements when the red or green signal lights were illuminated o Similar results seen in people with damage to premotor cortex. o Halsband and Freund (1990):  Found that patients with lesions in premotor cortex could learn to make 6 different movements in response to spatial cues, but not to arbitrary visual cues.  That is, they could learn to point one of six locations in which they had just seen a visual stimulus, but they could not learn to use a set of visual, auditory, and tactile cues to make particular movements. IMITATING AND COMPREHENDING MOVEMENTS: ROLE OF THE MIRROR NEURON SYSTEM: • Rizolatti et al (2000) Found that neurons in an area of the rostral part of the ventral premotor cortex in the monkey brain (area F5) became active when monkeys saw people or other monkeys perform various grasping, holding, or manipulating movements or when they performed these movements themselves.  Thus, the neurons responded to either the sight or the execution of particular movements.  Investigators named these cells mirror neurons. o The location of these neurons, the ventral premotor cortex, is reciprocally connected with the inferior parietal lobule, a region of the posterior parietal lobe, and further investigation found that this region also contains mirror neurons. o Given the characteristics of mirror neurons, we might expect that they play a role in a monkey’s ability to imitate the movements of other monkeys, which was found to be true by Rizolatti. o Mirror Neurons: Neurons located in the ventral premotor cortex and inferior parietal lobule that responds when the individual makes a particular movement or sees another individual making that movement. • Several fMRI studies have shown that the human brain also contains a circuit of mirror neurons in the inferior parietal lobule and the ventral premotor area.  EX: in a fMRI study, Buccino et al. asked nonmusicians to watch and then imitate video clips of an expert guitarist placing his finger son the nexk of a guitar to play a chord.  Investigators found that both watching and imitating the movements activated the mirror neuron circuit.  Studies have shown that the mirror neuron system is activated more strongly when one is watching a behavior in which one is already competent. • Mirror neurons are activated not only by the performance of an action or the sight of someone else performing that action, but also by sounds that indicate the occurrence of a familiar action.  Kohler et al. found that mirror neurons in the ventral pre-frontal cortex of monkeys became active when the animals heard sounds they recognized, such as peanuts breaking, a piece of paper being ripped, or a stick beign dropped.  Individual neurons-the researchers called them audiovisual neurons- responded to the sounds of particular actions and to the sight of those actions.  Presumably, activation of these neurons by these familiar sounds reminds the animals of the actions the sound represents.
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