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Chapter 8 Part2 (Pages 277-292)
Planning and Initiating Movement: Role of the Motor Cortex Association Cortex
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The supplementary motor area and the premotor cortex are involved in the planning of
movements and they execute these plans through their connections with the primary
motor cortex.
These regions become activated with people imagine or actually perform these actions.
The motor association cortex is also involved in imitating the actions of other people.
The supplementary motor area and the premotor cortex receive information from
association areas of the parietal and temporal cortex.
The visual association cortex is organized in two streams: dorsal and ventral.
o The ventral stream terminates in the inferior temporal cortex is involved and
perceiving particular objects (what stream)
o The dorsal stream, which terminates in the posterior parietal love, is involved in
the perception of location (where stream)
o The parietal lobe also organizes visually guided movement (how stream)
o Parietal lov e also receives information about spatial location from
somatosensory, vestibular and auditory systems and integrates it with information
from the visual cortex.
o The regions of the frontal cortex that plan movement receive info about
movements from the temporal and parietal lobe
o The pathway from parietal lobe to frontal lobe is important in locomotion and arm
and hand movements.
The Supplementary Motor Area
o Important in learnt and performed behaviours involving sequential movement
o Damage to this region disrupts well learnt sequences of responses (when the
performance of one response is the signal for the next response)
o Chen found that lesions of the supplementary motor cortex severely impaired
monkey`s ability to perform a simple sequence of two responses: pushing a lever
and then turning it to the left.
o Mushiake, Inase, Tanji trained monkeys to perform a set of responses pushing
each of 3 buttons in a certain sequence. When performed from memory, the
neurons in the SMA were activated. This was not the case when performed from
visual cues (the buttons lit up in the order they needed to be pressed)
o Shima and Tanji taught monkeys six sequences of three motor responses. They
then found neurons whose activity encoded elements of the sequences (I.e. If the
sequence was push, pull turn different neurons would light up for push and others
would light up for pull)
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o Shima and Tanji temporarily inactivated the monkeys’ neural area with a drug
that activated GABA receptors and inhibited the neurons and found that monkeys
could do the individual tasks with visual cues but not make a sequence.
o Hikosaka did a human study and instead of the drug used transcranial magnetic
stimulation the same thing occurred. However the disruption was not immediate,
the participants just did not “know” the next step after continuing the sequence for
one second.
o The SMA is involved in planning actions yet to come. The actual execution is
controlled by the primary motor cortex.
o The region anterior to the SMA is called the pre-SMA is involved in the control
of spontaneous movements, in the perception of control.
o When the SMA and preSMA stimulated, the DESIRE to move occurs, however
stimulation of the motor cortex occurs, involuntary movement is the result.
o Lau-functional imaging study found that the pre SMA became active just before
people performed spontaneous movement. (The participants made random
movements with their fingers while paying attention to a red light clock)
 They made the movement 0.2 seconds before the movement began
 The pre-SMA began to increase 2-3 seconds before that showing that the
decision occurred before the person was aware of it.
o The most important input to the supplementary motor area comes from the
parietal lobe
 Sirgu performed a similar experiment to Lau and investigated decision
making when the parietal cortex had lesions. They found that people with
partial lesions could report when they started the movement but were not
aware of an intention to move prior to making the movement.
 The information from the parietal lobe allows the pre-SMA to realize a
decision has been made
 People with prefrontal lesions will react to events but are deficit in
imitating behaviour so perhaps this is an important area for decision.
The Premotor cortex
o Involved in learning and executing complex movements that are guided by
sensory information
o Involved in using arbitrary stimuli to indicate what movement should be made
 E.g. reaching for an object we see in a particular situation involves nonarbitrary information
 E.g. Doing a particular movement when told to by a choreographer is
arbitrary (information that is not directly related to the movement that it
signals)
o Kurata and Hoffman trained monkeys to move their hands to the left or right in
response to a spatial or nonspatial signal.
 The spatial signal required a monkey to move in the direction indicated by
signal light located to the left and right of its hand.
 The non spatial signal consisted of a pair of lights, one red and one green,
located in the middle. The red light signalled a movement to the left and
the green to the right. The investigators temporarily inactivated the
premotor cortex and the monkeys could still move their hands toward a
signal light located left or right (non arbitrary signal) but could not make
an appropriate movement when the red or green lights were lit up.
o Halsband and Freund found that patients with these lesions could learn to make 6
different movements in response to spatial cues but not to arbitrary cues.
Imitating and Comprehending movements: Role of the Mirror Neuron System:
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Rizzolatti performed a study that discovered that neurons in the rostral part of the ventral
premotor cortex in the monkey brain (area F5) became active when monkeys saw people
or other monkeys performing various grasping/reaching/manipulating movements.
The neurons that responded to this are called mirror neurons-neurons that are in the
ventral premotor cortex and inferior parietal lobule (part of posterior parietal lobe) that
responds when an individual makes a movement or sees others making that movement.
Buccino asked non musicians to watch and then imitate an expert guitarist. They found
that both watching and playing activated mirror neurons
Calvo Merino had ballet dancers; capoeira dancers and non dancers watch videos of
capoeira and ballet. All subjects show activation in mirror neurons but the professions
had more activation.
Mirror neurons are also activated by sounds that indicate the occurrence of the action
(Kohler-monkeys mirror neurons were activated with the animal heard sounds such as a
peanut breaking).
Audiovisual neurons respond to the sounds and to sights of particular actions.
Lahav, Saltzman and Schlaug found the relation by teaching non-musicians how to play a
song. When the song was played, the audiovisual neurons were activated without them
playing it.
Haslinger found that the interaction worked in the other direction is well. They showed
professional pianists silent videos of the hand playing the piano and also meaningless
hand movements above the piano. They found that auditory cortex and mirror neuron and
visual cortex was activated for piano playing and the meaningless movements.
Rizzolatti, Fogassi and Gallese suggest that the mirror neuron helps us understand others
actions.
Iaacoboni suggests that mirror neurons help us understand others’ intentions. This was
shown by showing clips of an arm and hand researching for and grasping a mug. The clip
was shown in isolation or in context with snack items such as mug , milk, jam, cookies
etc) or after the eating where the cookies have been eaten and the jam opened.
The first context suggests that the intent is that of drinking and the second shows an
intention of cleaning. There was a difference in the activation between contexts when the
movement of gripping a mug occurred in each.
Control of Reaching and Grasping:
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Connections between frontal and parietal lobe critical
Parietal reach region-a region in the medial posterior parietal cortex that plays a critical
role in pointing and reaching with the hands
The anterior part of the intraparietal sulcus (aIPS) is critical in controlling hand and
finger movements involving in grasping the object.
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Frey had people reach for objects of different shapes which required different figure and
hand movements to grasp. The brain activity related to grasping was determined by
subtracting the areas produced for reaching for and touching from the reaching for and
grasping activation
Tunik, Frey and Grafton confirmed the importance of the aIPS. The subjects had to reach
and grasp a rectangular object that was oriented with its long side vertical or horizontal.
On some trials, the object rotated which made the subjects have to change their hand
position before they grabbed it. Some of the trails involved the transcranial magnetic
stimulation disrupting the aIPS. After 65 ms of the rotation the accuracy of changing grip
before grabbing was decreased.
No other stimulation of primary motor or parietal lobe had an effect there
The aIPS is from the dorsal stream of vision.
Shmuelof and Zohary-subjects watched videos of a hand reaching to grab various objects,
sometimes with it in the right or left visual field, sometimes the objects and hand location
were switched. (subjects fixated on a central point)
This procedure means that for a particular trial, information was alternated between the
hemispheres with one side with object info and one side with hand info. Analysis of the
brain activation showed that the information about the object activated ventral stream and
hand info activated aIPS.
Deficits of Skilled Movements: The Apraxias
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Damage to the frontal or parietal cortex on the left side produces apraxia
Apraxia-difficulty in carrying out purposeful movements in the absence of paralysis or
muscular weakness.
Apraxias refers to the inability to imitate movements or produce them in response to
verbal instruction inability to demonstrate the movement that would be made in using a
familiar tool or utensil.
Four types: limb (problems with hands, arms, fingers), oral(movements of muscles used
in speech), apraxic (particular type of writing deficit), constructional (drawing or
constructing objects)
Limb Apraxia:
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Characterized by movement of the wrong part of limb, incorrect movement of right part
or right movement in the wrong sequence.
Assessed by asking patients to make specific movements.
Without having a real object to manipulate, a person must comprehend the command and
be able to imagine the article and make the proper movements.
Sometimes, with an actual object, patients can copy the hand movements.
Damage to the left parietal hemisphere causes apraxia of both hands because the right
hemisphere is involved with extra personal space and the left is with one’s own body.
Chaminade, Meltzoff and Dectey-asked subjects to watch another person perform
hand/arm gestures and then imitate them or make different ones with the same arm or
different arm. The posterior regions of the right hemisphere traced the model in space and
the left parietal love organized the response movement.
The frontal cortex is more important that the parietal lobe in recognizing meaning.
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Pazzaglia tested patients with damage to the left and others with damage to the right
hemisphere.. And found that 2/3 of the ones with left hemisphere damage had limb
apraxia. They tested them for recognition of hand gestures in which a person would
perform a gesture correctly or incorrectly. Apraxic patients with damage to the inferior
frontal gyrus but not to the parietal cortex couldn’t understand the meanings of gestures
well.
Constructional Apraxia
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Caused by lesions of the right hemisphere, particularly in the right parietal lobe
People with this disorder generally do not have problems making most types of skilled
hand and arm movements such as imitation, using objects or pretending to use them
They have trouble drawing pictures or assembling objects (such as lego).
Involves the ability to perceive and imagine geometrical relations.
Basal Ganglia
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Motor nuclei includes the caudate nucleus, the putamen and globus pallidus.
Caudate nucleus-a telencephalic nucleus, one of input nuclei of basal ganglia, involved in
voluntary movement
Putamen-telencephalic nucleus, one of the input nuclei of the basal ganglia, involved with
control of voluntary movement
Globus pallidus-a telencephalic nucleus, the primary output nucleus of basal ganglia,
involved in voluntary movement
Receives most of the input from all regions of cerebral cortex (especially from primary
motor and somatosensory cortexes) and the substantia nigra.
They have 2 primary outputs-the primary motor cortex and the supplementary motor area
and the premotor cortex and motor nuclei of the brain stem that contribute to
ventromedial pathways.
Ventral anterior nucleus of thalamus-a thalamus nucleus that receives projections from
the basal ganglia and sends projections to the motor cortex
Ventrolateral nucleus of thalamus-a thalamus nucleus that receives projections from the
basal ganglia and sends projections to the motor cortex
The frontal parietal and temporal cortex sends axons to the caudate nucleus and the
putamen which then connect with the globus pallidus.
The globus pallidus sends info to the motor cortex via the ventral anterior and
ventrolateral nucleus of the thalamus,
The basal ganglia can monitor somatosensory information and are informed of
movements being planned and executed by the motor cortex
The substantia nigra is important in communication with the basal ganglia-the
degeneration of the nigrostriatal bundle (the dopaminergic pathway from the substantia
nigra to the caudate nucleus and the putamen) causes Parkinson’s disease
The links in the loop of the cortical basal ganglia are made by both excitatory (glutamate
secreting) and inhibitory (gaba secreting) neurons
The caudate nucleus and putamen receive excitatory input from the cerebral cortex. They
send inhibitory axons to the external and internal region of the globus pallidus. (GPi and
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GPe) The direct pathway includes GPi. Neurons in the GPi send inhibitory axons to the
ventral anterior and ventrolateral thalamus which sends excitatory projections to the
motor cortex.
The pathway that includes the GPe is known as the indirect pathway
o Indirect pathway-the pathway that includes the caudate nucleus and putamen, the
external division of the globus pallidus, the subthalmic nucleus, the internal
division of the globus pallidus and the ventral anterior/ventrolateral thalamic
nuclei: has an inhibitory effect on movement.
o Direct pathway: includes caudate nucleus, putamen, internal division of the
globus pallidus and the ventral anterior/ventrolateral thalamic nuclei has an
excitatory effect on movement.
Neurons in the GPe send inhibitory input to the subthalmic nucleus which sends
excitatory to the GPi which results in the same circuit described for the GPi but the
overall effect on the motor cortex is INHIBITORY.
The GP also sends axons to various motor nuclei in the brain stem that contributes to the
ventromedial system.
Parkinson’s disease:
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Symptoms: muscular rigidity, slowness of movement, a resting tremor and postural
instability.
Damage to the nigrostriaral bundle causes this because normal movement requires a
balance between direct and indirect pathways. The caudate nucleus and putamen consist
of 2 different zones which receive input from dopaminergic neurons from substantia
nigra. One of these zones contains D1 dopamine receptors which produce excitatory
effects. Neurons in this zone send input to GPi.
Neurons in the other zone contain D2 receptors which send input to GPe which produces
inhibitory effects. A decrease in this circuit probably causes the poor muscle rigidity and
posture control.
The standard treatment for Parkinson’s is L-DOPA (the precursor to dopamine)
The increased amount of dopamine lets the remaining nigrostriatal dopaminergic neurons
produce and release more dopamine
However this causes dyskinesais and dystonas-involuntary movements and postures are
presumably caused by too much stimulation of the dopamine receptors in the basal
ganglia
Also this treatment does not last forever
Huntington’s disease
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A fatal inherited disorder that causes degeneration of the caudate nucleus and putamen:
characterized by uncontrollable jerking movements, writhing movements and dementia.
Causes degeneration of caudate nucleus and putamen especially of GABAergic and
acetylcholiergic neurons
Causes uncontrollable movements, especially jerky limb movements.
The movements of Huntington’s’ disease look like fragments of purposeful movements
but are involuntary.
Progressive, eventually causes death
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Usually begins in 30s of 40s
First signs of neural degeneration occur in the caudate nucleus and putamen-in the
medium sized spiny inhibitory neurons whose axons travel to the GPe.
The loss of inhibition provided by these GABA secreting neurons increases activity in
GPe which then inhibits the subthalamic nucleus. Thus the activation in the GPi
decreases and excessive movements occur.
As the disease progresses the caudate nucleus and the putamen decrease until they barely
exist. The patient dies from complications of immobility.
There is no cure.
Hereditary caused by a dominant gene on chromosome 4.
Defect identified as a repeated sequence of bases that code for amino acid glutamine.
Longer stretches of glutamine are found in people that symptoms appear at in a younger
age.
The Cerebellum
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Part of motor system
50 billion neurons compared to 22 billion in the cerebral cortex.
Projects to every major motor structure of the brain
When it is damaged, peoples movements become jerky, erratic and uncoordinated.
Consists of 2 hemispheres that contain several deep nuclei situated beneath the wrinkled
and folded cerebellar cortex.
The medial part of the cerebellum is phylogenetically older than the lateral part and is in
the control of the ventromedial system.
The flocculonodular lobe, located at the caudal end of the cerebellum, helps control
postural reflex.
o Receives input from the vestibular system and projects axons to the vestibular
nucleus
the vermis-located on the midline, receives auditory and visual info from the tectum and
the cutaneous and kinaesthetic info from the spinal cord and sends output to the fastigial
nucleus
o the fastigial nucleus: a deep cerebellar nucleus involved in the control of
movement by the reticulospinal and vestibulospinal tracts
Neurons in the fastigial nucleus send axons to the vestibular nucleus and to motor nuclei
in the reticular formation.
The rest of the cerebellar cortex receives most of its input from the cerebral cortex
including the primary motor cortex and the association cortex.
o This input is relayed to the cerebellar cortex through the pontine tegmental
reticular nucleus.
The intermediate zone of the cereballar cortex projects to the interposed nucleus which
projects to the red nucleus.
The immediate zone influences the control of the rubrospinal system over movements of
the arms and legs.
The interposed nucleus also sends outputs to the ventrolateral thalamic nucleus which
projects to the motor cortex.
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The lateral zone of the cerebellum is involved in the control of independent limb
movements especially in rapid, skilled movements
o These movements are initiated by neurons in the frontal association cortex.
o However, though the frontal cortex plans and initiates movements it does not have
the neural circuitry to calculate the complex sequences needed for skilled
movements. The lateral zone of the cerebellum does this.
Both the frontal association cortex and the primary motor cortex send info about intended
movement to the lateral cerebellum through the pontine nucleus. The lateral zone also
gets info from the somatosensory system which tells it about limb position and rate of
movement.
When the cerebellum has the info that the motor cortex has initiated a movement, it
computes what the muscles will need to do to perform this reaction. This info is sent to
the dentate nucleus which is another cerebellar nucleus. Neurons there pass the info to the
ventrolateral thalamus which sends the info to the primary motor cortex.
To humans, lesions of different regions of the cerebellum produce different symptoms.
o Damage to the flocculondular lobe or the vermis causes disturbances in posture
and balance
o Damage to the intermediate zone produces deficits in movement controlled by the
rubrospinal cord-limb rigidity
o Damage to the lateral zone results in decomposition of movement (i.e. rough
movement, separate movements by joints such as someone trying to bring their
hand to their mouth will make separate movements with the joints of shoulder,
elbow and wrist)
o Damage to the lateral zone also impair the timing of rapid ballistic (throwing)
movements.
o Kornhuber suggested that one of the primary functions of the cerebellum is timing
the duration of rapid movements.
o Timmann, Watts and Hore: when tossing a ball at a target using an overarm
throw, a person raises his hand above the shoulders, rotates the arm forward and
then releases the ball by extending the fingers and moving them apart. The
researchers found that normal subjects released the ball within an 11 msec
window while patients with cerebellar lesions did 5 times worse. Their window
was 55 msec wide.
The cerebellum also integrates successive sequences of movements that must be
performed one after another.
o Holmes reported that the patient can move an unaffected arm subconsciously but
must think out the movements of affected arms.
o Thach obtained experimental evidence that corroborates this role. He found many
neurons in the dentate nucleus showed response patterns that predicted the next
movement in a sequence rather than the one that was currently taking place.
Reticular Formation
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Consists of a large number of nuclei located in the core of the medulla, pons and
midbrain
Controls activity of the gamma motor system and regulates muscle tonus
Pons and medulla contain several nuclei with specific motor functions
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o Control automatic or semiautomatic responses such as respiration, sneezing,
coughing and vomiting
Ventromedial pathways originate in the superior colliculi, vestibular nuclei and reticular
formation.
The reticular formation plays a role in control of posture
Plays a role in locomotion
Stimulation of the mesencephalic locomotor region, located ventral to the inferior
colliculus, causes a cat to make pacing movements
o This region does not send fibres to the spinal cord but controls the activity of
reticulospinal tract neurons.
Sigeal and McGinty recorded in 35 neurons in the reticular formation of unanathesticized
free moving cats. 32 of these neurons responded during specific movements of the head,
tongue, facial muscles, ears, forepaw or shoulder. The specific nature suggests these
neurons play a role in controlling movement.