3.6C neuropsychologie
Colleges + literatuur
, Literature week 1: perception & motor
system
Kolb chapter 9: organization of the motor system
The term motor system is usually reserved for those parts of the nervous system
that take part most directly in producing movement and for the spinal-cord neural
circuits that issue commands to muscles through the peripheral nerves.
4 neocortical regions (in the FRONTAL LOBE) produce our skilled movements:
1. The posterior cortex specifies movement goals and sends sensory
information from vision, touch and hearing into the frontal regions via
multiple routes. Direct routes primary motor cortex. More conscious
control temporal and frontal cortex.
2. The prefrontal cortex generates plans for movements that is passes
along to the premotor and motor cortex.
3. The premotor cortex houses a movement repertoire – its lexicon – that
recognizes others’ movements and selects similar or different actions.
4. The lexicon of the primary motor cortex consists of more-elementary
movements that the premotor lexicon, including hand and mouth
movements.
Large parts of the motor cortex regulate hand, finger, lip and tongue movements,
giving us precise, fine motor control over those body parts. Parts of the body over
which we have much broader control have a much smaller representation in the
motor cortex Penfield’s homunculus. Another distinctive feature of the
homunculus is the arrangement of body parts in relation to that of the real body.
However, many cortical maps of the body exist, but each map represents a
different action, the part of space in which an action is to take place, and that
action’s intended function. This cortical map is also proposed to be quite flexible
Graziano’s topography
In general, Graziano is consistent with Penfield’s map and with the idea that
whole-body movements are represented in the premotor cortex and more
discrete movements in the motor cortex.
,The motor cortex is not the only region from which movements can be evoked.
Similar functional movements can be elicited by the parietal cortex. Anatomical
studies of the relationship between the topographical regions of the motor cortex
and the matching parietal regions show that they have dense anatomical
connections.
For example: Sensory information must be sent from the visual cortex to the
motor cortex Based on information about object location, the visual cortex
instructs the parietal arm region about the object’s location and the hand region
about how to shape the digits to grasp the object The reach and grasp regions
of the parietal cortex then connect to reach and grasp regions of the motor
cortex that will produce the movement over descending pathways to the spinal
cord.
Thus, the connections from visual cortex to parietal cortex to motor cortex
constitute a dual pathway that produces the action of grasping the target.
Each cortical motor region makes a different contribution to movement. The
visual cortex identifies the spatial location of the target and its shape. The
parietal cortex identifies the body part that will contact the object. The motor
cortex in turn represents the elements required to move the arm to the target
and shape the digits to grasp it.
The movement lexicon
The study by Graziano supports the idea that humans have a prewired
movement lexicon in the brain, meaning certain movement patterns are
encoded rather than entirely learned. This is evident in the universal use of the
pincer grip, which appears in infants and is also common among primates.
Lesions in the motor cortex can disrupt whole coordinated movements rather
than just affecting individual muscles, further supporting the existence of this
lexicon.
The premotor cortex, which has a common but more complex movement
repertoire than the primary motor cortex (M1), plays a crucial role in coordinating
whole-body movements. M1 controls more specific acts. Damage to this area can
disrupt complex tasks requiring coordination between limbs, such as retrieving an
object using both hands. This suggests that learning new motor skills involves
modifying preexisting movement patterns.
Studies by Evarts and Georgopoulos show that populations of neurons in the
motor cortex are involved in both planning and executing movements. these
neurons begin to discharge even before movement: they participate in planning
the movement as well as initiating it. The neurons continue to discharge during
the movement, confirming that they also play a role in executing it. The neurons
also discharge at a higher rate when the movement is loaded with a weight, an
indication that motor-cortex neurons increase the force of a movement by
increasing their firing rate.
Evarts’s results also reveal that the motor cortex specifies movement direction.
Neurons in the motor-cortex wrist area discharge when the monkey flexes its
wrist to bring the hand inward but not when it extends its wrist to move the hand
back to its starting position. These neuronal on–off responses, depending on
, whether the wrist is flexed toward the body or extended away, are a simple way
of encoding the direction in which the wrist is moving.
Mirroring movement
Our movements are anything but robotic. Our actions are learned, situation
specific, and often dependent upon our interactions with others. Mirror system
neurons, discovered in monkeys by Umilta and colleagues (2001), fire both when
an individual performs an action and when they observe the same action
performed by others. These neurons, located in the ventral premotor cortex,
encode the goal of an action rather than just the movement itself. Some are
highly specific, responding only to particular hand movements or object sizes,
while others are more flexible, recognizing actions even when parts of them are
obscured. Thus, the target of the action is more important to these mirror
neurons than are the details of the action required to obtain it.
In humans, the mirror neuron system is more complex, involving Broca’s area and
other brain regions. This system plays a key role in understanding others' actions,
social awareness, and even language development. Mirror neurons allow us to
internally simulate observed movements, our cognitive understanding of an
action is embodied in the neural systems that produce that action. Dysfunction in
this system may be linked to conditions like autism, where social understanding
and empathy are impaired. The human mirror neuron system is more advanced
than that of monkeys, likely due to our greater reliance on mimicry and language.
The brainstem: motor control
The brainstem and basal ganglia play essential roles in movement control. The
brainstem, beyond transmitting signals from the cortex to the spinal cord, is
responsible for whole-body movements, posture, balance, and autonomic
functions. Swiss neuroscientist Walter Hess demonstrated that stimulating the
brainstem in animals could trigger various instinctive behaviours, such as
jumping, walking, or grooming, showing its role in innate movement patterns.
The basal ganglia and movement force
The basal ganglia, a group of subcortical structures in the forebrain, connect the
motor cortex with the midbrain and connect the sensory regions of the neocortex
with the motor cortex to help regulate movement force.
A prominent structure of the basal ganglia is the caudate putamen, a large
cluster of nuclei located beneath the frontal cortex. The basal ganglia receive
inputs from two main sources: (1) All areas of the neocortex and limbic cortex,
including the motor cortex, project to the basal ganglia. (2) The nigrostriatal
dopamine pathway extends into the basal ganglia from the substantia nigra, a
cluster of darkly pigmented cells in the midbrain. The basal ganglia send
projections back ot both the motor cortex and the substantia nigra.
Colleges + literatuur
, Literature week 1: perception & motor
system
Kolb chapter 9: organization of the motor system
The term motor system is usually reserved for those parts of the nervous system
that take part most directly in producing movement and for the spinal-cord neural
circuits that issue commands to muscles through the peripheral nerves.
4 neocortical regions (in the FRONTAL LOBE) produce our skilled movements:
1. The posterior cortex specifies movement goals and sends sensory
information from vision, touch and hearing into the frontal regions via
multiple routes. Direct routes primary motor cortex. More conscious
control temporal and frontal cortex.
2. The prefrontal cortex generates plans for movements that is passes
along to the premotor and motor cortex.
3. The premotor cortex houses a movement repertoire – its lexicon – that
recognizes others’ movements and selects similar or different actions.
4. The lexicon of the primary motor cortex consists of more-elementary
movements that the premotor lexicon, including hand and mouth
movements.
Large parts of the motor cortex regulate hand, finger, lip and tongue movements,
giving us precise, fine motor control over those body parts. Parts of the body over
which we have much broader control have a much smaller representation in the
motor cortex Penfield’s homunculus. Another distinctive feature of the
homunculus is the arrangement of body parts in relation to that of the real body.
However, many cortical maps of the body exist, but each map represents a
different action, the part of space in which an action is to take place, and that
action’s intended function. This cortical map is also proposed to be quite flexible
Graziano’s topography
In general, Graziano is consistent with Penfield’s map and with the idea that
whole-body movements are represented in the premotor cortex and more
discrete movements in the motor cortex.
,The motor cortex is not the only region from which movements can be evoked.
Similar functional movements can be elicited by the parietal cortex. Anatomical
studies of the relationship between the topographical regions of the motor cortex
and the matching parietal regions show that they have dense anatomical
connections.
For example: Sensory information must be sent from the visual cortex to the
motor cortex Based on information about object location, the visual cortex
instructs the parietal arm region about the object’s location and the hand region
about how to shape the digits to grasp the object The reach and grasp regions
of the parietal cortex then connect to reach and grasp regions of the motor
cortex that will produce the movement over descending pathways to the spinal
cord.
Thus, the connections from visual cortex to parietal cortex to motor cortex
constitute a dual pathway that produces the action of grasping the target.
Each cortical motor region makes a different contribution to movement. The
visual cortex identifies the spatial location of the target and its shape. The
parietal cortex identifies the body part that will contact the object. The motor
cortex in turn represents the elements required to move the arm to the target
and shape the digits to grasp it.
The movement lexicon
The study by Graziano supports the idea that humans have a prewired
movement lexicon in the brain, meaning certain movement patterns are
encoded rather than entirely learned. This is evident in the universal use of the
pincer grip, which appears in infants and is also common among primates.
Lesions in the motor cortex can disrupt whole coordinated movements rather
than just affecting individual muscles, further supporting the existence of this
lexicon.
The premotor cortex, which has a common but more complex movement
repertoire than the primary motor cortex (M1), plays a crucial role in coordinating
whole-body movements. M1 controls more specific acts. Damage to this area can
disrupt complex tasks requiring coordination between limbs, such as retrieving an
object using both hands. This suggests that learning new motor skills involves
modifying preexisting movement patterns.
Studies by Evarts and Georgopoulos show that populations of neurons in the
motor cortex are involved in both planning and executing movements. these
neurons begin to discharge even before movement: they participate in planning
the movement as well as initiating it. The neurons continue to discharge during
the movement, confirming that they also play a role in executing it. The neurons
also discharge at a higher rate when the movement is loaded with a weight, an
indication that motor-cortex neurons increase the force of a movement by
increasing their firing rate.
Evarts’s results also reveal that the motor cortex specifies movement direction.
Neurons in the motor-cortex wrist area discharge when the monkey flexes its
wrist to bring the hand inward but not when it extends its wrist to move the hand
back to its starting position. These neuronal on–off responses, depending on
, whether the wrist is flexed toward the body or extended away, are a simple way
of encoding the direction in which the wrist is moving.
Mirroring movement
Our movements are anything but robotic. Our actions are learned, situation
specific, and often dependent upon our interactions with others. Mirror system
neurons, discovered in monkeys by Umilta and colleagues (2001), fire both when
an individual performs an action and when they observe the same action
performed by others. These neurons, located in the ventral premotor cortex,
encode the goal of an action rather than just the movement itself. Some are
highly specific, responding only to particular hand movements or object sizes,
while others are more flexible, recognizing actions even when parts of them are
obscured. Thus, the target of the action is more important to these mirror
neurons than are the details of the action required to obtain it.
In humans, the mirror neuron system is more complex, involving Broca’s area and
other brain regions. This system plays a key role in understanding others' actions,
social awareness, and even language development. Mirror neurons allow us to
internally simulate observed movements, our cognitive understanding of an
action is embodied in the neural systems that produce that action. Dysfunction in
this system may be linked to conditions like autism, where social understanding
and empathy are impaired. The human mirror neuron system is more advanced
than that of monkeys, likely due to our greater reliance on mimicry and language.
The brainstem: motor control
The brainstem and basal ganglia play essential roles in movement control. The
brainstem, beyond transmitting signals from the cortex to the spinal cord, is
responsible for whole-body movements, posture, balance, and autonomic
functions. Swiss neuroscientist Walter Hess demonstrated that stimulating the
brainstem in animals could trigger various instinctive behaviours, such as
jumping, walking, or grooming, showing its role in innate movement patterns.
The basal ganglia and movement force
The basal ganglia, a group of subcortical structures in the forebrain, connect the
motor cortex with the midbrain and connect the sensory regions of the neocortex
with the motor cortex to help regulate movement force.
A prominent structure of the basal ganglia is the caudate putamen, a large
cluster of nuclei located beneath the frontal cortex. The basal ganglia receive
inputs from two main sources: (1) All areas of the neocortex and limbic cortex,
including the motor cortex, project to the basal ganglia. (2) The nigrostriatal
dopamine pathway extends into the basal ganglia from the substantia nigra, a
cluster of darkly pigmented cells in the midbrain. The basal ganglia send
projections back ot both the motor cortex and the substantia nigra.
