This summary offers a comprehensive overview of all the literature covered in block 3.6 Neuropsychology. It includes additional graphics illustrating the structure of the brain. The literature is summarised and organised in a detailed, yet concise manner. Everything you need to prepare for the exam...
,Week I: Perception & Motor System
ORGANISATION OF THE MOTOR SYSTEM (see image at the end of the problem)
Þ motor system – those parts of the NS that take part most directly in producing movement
and for the spinal-cord neural circuits that issue commands to muscles through the
peripheral nerves
The Neocortex: Initiating Movement
Þ the neocortex: initiating movement
o posterior cortex (lying posterior to the central fissure) – specifies movement goals
and sends sensory information from touch, vision, and hearing into the frontal regions
via multiple routes
• more direct routes: prompt the primary motor cortex to execute relatively
automatic movements
• indirect routes: information about movements requiring conscious control takes
indirect routes through the temporal and frontal cortex
o prefrontal cortex (on instructions from the posterior cortex) generates plans for
movements that it passes along to the premotor and motor cortex
o the premotor cortex immediately anterior to M1 houses a movement repertoire
• recognizes others’ movements and selects similar or different actions
o lexicon of the primary motor cortex (M1) – consists of more elementary movements
incl., hand, and mouth movements
o simplicity of movement
• if movement: relatively simple à premotor and motor cortex execute the action
• if planning is required à temporal and prefrontal cortices make decisions and then
the premotor and motor cortices execute the appropriate movements
Þ mapping the motor cortex
o most induced movements were triggered by stimulation of the primary motor cortex
• movement can also be produced by stimulation of dorsal part of premotor cortex
o body: symmetrical à each hemisphere contains an almost mirror-image representation
of the homunculus (“little human”)
o Penfield’s motor homunculus – upside down relative to the actual body
• movements are topographically organized in the primary motor cortex
§ electrical stimulation of the dorsomedial regions of M1 elicits movements in
the lower limbs
§ stimulation in ventral regions produces movements in the upper body, hands,
and face
• disproportionate relative sizes of body parts – most striking homuncular feature
§ size distortions reflect the fact that large part of the motor cortex regulate
hand, finger, lip, and tongue movements giving us precise motor control
, • there may be as many as 10 homunculi within the motor and premotor cortices
Þ natural movement categories – stimulation elicits “etiological categories of movement”
à the motor system is organised into specific cortical areas for different movements
o each region: 3 types of organisationà the body part to be moved; the spatial location
to which the movement is directed ;the movement’s function
o whole-body movements are represented in the premotor cortex
o more discrete movements are represented in the motor cortex
Þ visual-parietal-motor connections
o motor cortex is not the only region from which movements can be evoked
• electrically stimulating the parietal cortex and the parietal topography mirrors the
motor homunculus
o stepping movements – elicited from more dorsal parietal regions
o reaching movements – elicited from medial parietal regions
o hand and mouth movements – elicited from more ventral parietal regions
o visual, somatosensory, and/or auditory information about the target must be sent to the
motor cortex
o each cortical region makes a different contribution to movement
• visual cortex: identifies the spatial location of the target and its shape
§ instructs parietal arm region
• parietal cortex identifies the body part that will contact the object
§ parietal regions = sensory receptors
§ connect to reach and grasp regions of the motor cortex
• motor cortex: represents the elements required to move the arm to the target and
shape the digits to grasp it
§ will produce the movement over descending pathways to the spinal cord
• movements themselves may be orchestrated int eh brainstem or in the spinal cord
o reaching for an object employs 2 mechanisms (directing the hand to target and shaping
the fingers to grasp the target)
• 2 channels mediate the reach and grasp using dual pathways:
§ from visual cortex à parietal cortex à premotor cortex à motor cortex
Þ the movement lexicon – repertoire of movement categories in the cortex
o pincer grip (thumb + index finger) vs whole-hand grip
o people who have incurred small lesions of the motor cortex around the thumb region
of homunculus have weakness in the thumb, other fingers, and in the arm
• lesions impair not the hand or individual digit muscles but rather the coordinated
action of reaching for and grasping an object
o premotor cortex and the primary motor cortex share a common movement lexicon
• the repertoire available to the premotor cortex is more complex than that of M1
• damage to premotor cortex – disrupts more complex movements
• premotor cortex plays a greater role in organising whole-body movements than
M1, which controls specific acts
o basic movements elicited in the motor cortex can be extended to other actions through
learning by recruiting neural circuity used for more basic action
o learning to move entails learning how to use preorganised movement patterns to
achieve both skill and strength à blend together motor reflexes to form learned skilled
actions
o how are motor cortex cells involved in movement
• participate in planning the movement, initiating it, executing it
• they increase the force of a movement by increasing their firing rate
, • the motor cortex specifies movement direction
o movements are not produced simply by the action of a single cell but rather by the
coordinated activity of populations of cells
• motor cortex à each neuron is maximally active when the monkey moves its arm
in a particular direction
§ as it moves arm in directions other than the one to which a particular cell
maximally responds, the cell decreases its activity in proportion to the
displacement from the “preferred direction”
• the motor cortex calculates both the direction and the distance of movements
Þ mirroring movement
o actions: learned, situation-specific, often dependent upon interactions w/ others
o remarkable finding: subset of neurons in the ventral premotor area discharge not only
when the monkey itself makes a movement but also discharge in much the same way
when the monkey sees other monkeys make the same movement and when people
make the same movement
o mirror system neurons à encode the goal of an action
• do not respond to objects, isolated hand movements, pictures/videos of movement
• some have very exacting requirements
• others more broadly tuned and continue to respond when e.g.: grip pattern changes
• target of the action is more important to these mirror neurons than are the details
of the action required to obtain it
Þ map of mirror neurons
o core mirror neuron system (yellow) – sensitive to
transitive movements; comprises the inferior frontal
cortex (IFG), ventral premotor cortex (PMV), and
inferior parietal cortex (IPL)
• Broca’s area
o distributed mirror neuron system responds to:
• hand movements (purple) in the dorsal premotor
cortex (PMD), superior parietal lobe (SPL)
• upper limb movements (blue) in portion of the
superior temporal sulcus (STS)
• tool use (orange)
• intransitive movements in which no object is
manipulated (green)
Þ flexible properties of mirror neurons underlie our ability to imagine movements and allows
us to control BCIs, ability to understand the actions of others; higher cognitive functions
o mirror neurons form the substrate for self-awareness, social awareness, awareness of
intention and action of others; likely important for gestural and verbal language
o some symptoms of some disorders are related to the mirror neuron system (e.g.:
absence of empathy)
Þ mirror neuron theory – we understand our own actions and those of others by internally
replicating the movements we would use to produce that action
o our cognitive understanding of an action is embodied in the neural systems that
produce that action
The Brainstem: Motor Control
Þ the brainstem: motor control
o about 26 pathways to the spinal cord originate in various brainstem locations
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