Lecture 5

Question 1

what section of the sensory-motor organisation hierarchy is the primary motor cortex?

Answer 1

programming

Question 2

what is the primary motor cortex?

Answer 2

develops motor programs and sends motor commands to the muscles

Question 3

where in the sensory-motor organisation hierarchy is the pre-motor areas?

Answer 3

planning

Question 4

what do the pre-motor areas do?

Answer 4

planning and selecting those motor programs that the primary motor cortex laters develops and sends out

Question 5

what are the four lobes in the brain from front to back?

Answer 5

frontal lobe
parietal
occipital lobe
temporal lobe

Question 6

where and what is the dorsolateral prefrontal associative cortex?

Answer 6

front of the brain

involved in action selection and action planning

important for decision making in early stages of motor control

Question 7

what does dorsal and ventral mean?

Answer 7

dorsal - on top
ventral - below

Question 8

where and what is the supplementary motor cortex?

Answer 8

midline structure in the middle of the brain that is also involved in actual planning and sequencing

Question 9

where and what is the posterior parietal cortex (area 5 area 7)?

Answer 9

top back of the brain

important sensory and motor function

Question 10

where and what is the somatosensory cortex?

Answer 10

in the middle of the brain

involved in processing feedback that returns back from the muscles

Question 11

what is the cerebral cortex?

Answer 11

Cerebral cortex (grey matter) is the outer layer of the brain, and it covers many deeper subcortical regions, such as the thalamus or the hippocampus

Question 12

how many layers are in the cerebral cortex?

Answer 12

6 layers or laminaes

Question 13

what is the purpose of the layers?

Answer 13

Each of these layers have different cell types, and each of these cell types receive specific inputs and specific outputs where these neurones terminate

They define different regions of the cerebral cortex that have separate functions

Question 14

which layer is the key input layer?

Answer 14

layer 4

Question 15

which layers are the key output layers?

Answer 15

layers 5 and 6

Question 16

which layers have cells that are really large?

Answer 16

Cells in layers 3 and 5 are really large and a really defining feature of the primary motor cortex because they’re critical for the execution of voluntary movement

Question 17

which neuranatomist discovered 52 different areas with cytoarchitectural differences?

Answer 17

Brodmann

Question 18

Was Brodmans maps supported and relevant?

Answer 18

Anatomical distinction (Brodmann) is functionally relevant

Brodmann discovered 52 areas based on the profiles of different cells

Brodmann’s scales of different brain areas is a very useful scale of differentiation

Question 19

Which area contains a specific type of pyramidal cells?

Answer 19

M1area contains Betz cells in layer 5 (one of two output layers)

key characteristic

Question 20

how do cortical projections occur?

Answer 20

• Betz cells - large pyramidal cells
• Project from motor cortex to spinal tract (cortical tract neurons)
  ^through the spinal cord there are direct connections to muscles and different parts of the body
• Only 5% project to motor-neurons; the rest reach spinal interneurons
• Betz cells also project to brain-stem

Question 21

what is the technical term for the spinal tract?

Answer 21

corticospinal tract

Question 22

how do Betz cells interact with the corticospinal tract?

Answer 22

• Betz cells from the motor cortex initiate, regulate and control voluntary skilled movements by innervating alpha and gamma motor neurons in the spinal cord
• Provides conscious voluntary control of skeletal muscles
• Tract crosses at the medulla (base of the skull), so limb movements are controlled by the contralateral motor cortex (left goes to the right and right goes to the left, AKA left motor cortex controls the right side of your body and vice versa)

Question 23

how do we generally map the motor cortex?

Answer 23

• Discovered electrical stimulation causes simple movements
• Map established (and cartooned ever after)
• This can also be seen in humans…

Interesting aspect of the motor cortex is that it has a somatic topic representation of different body parts
Meaning that different parts of the primary motor cortex send motor commands to different parts of the human body

Different areas of the body seemingly demand different amounts of motor control

Muscles in the face or tongue for example would demand a much more finer motor control than say your leg or back

AKA different parts of the motor cortex are related to different parts of the body

Question 24

how are sensory and motor maps connected?

Answer 24

• Close mirror relationship between sensory & motor maps
• Multiple maps: maps reflect sensory-motor specialisation

A very strong relationship between somatotopic maps that you have in the primary motor cortex and in the muscle sensory cortex

Motor cortex is involved in sending out motor commands and somatosensory cortex is involved in receiving feedback from the muscles

The key thing here is that both regions have a very strong relationship in terms of specialisation for particular muscle groups

Question 25

is there any evidence against the motor maps we know?

Answer 25

Cortical motor maps are actually far less "realistic" than the cartoons imply They are not the only thing that determines the organisation of the primary motor cortex Subsequent research has discovered a lot more overlap between the representation of different body parts than would be expected if this were the only principle that determines organisations of neurones

Question 26

what are effector-specific regions?

Answer 26

Effector-specific regions are interdigitated with regions showing different connectivity, structure, and function

Question 27

what are inter-effector regions?

Answer 27

Inter-effector regions that show high connectivity to each other and to cingulo-opercular network Inter-effector regions become active during planning (rather than execution) and lack effector specificity

Question 28

what is represented in the motor cortex, muscles or movement?

Answer 28

* Initially thought that the primary motor cortex just encodes specific muscle activity, kind of like the activity of particular sets of neurones. Just represents which kind of muscles in the body will become active * Suggesting that external electrical stimulation of particular neurones should just induce invariant activity * Only been found with Brief micro-stimulation (50ms): ○ Simple movements / contractions of contralateral muscles * Prolonged stimulation: ○ Complex goal-directed actions

Question 29

describe the precision grip vs skilled use of fingers study

Answer 29

In the study above, they trained monkeys to do two types of actions Either a precision grip, somewhere there they really have to exert more fine motor control using two different fingers in a more nuanced way, or a power grip (where they just apply brute force to a level) They were recording muscle activity with EMG How does the recruitment of neurones in the primary motor cortex differ between these two types of movements? Is it a function of the force that you're applying or is it a function of the extent of dexterity? Results showed it seems relatively easy for the brain to send a motor command for relatively coarse movements applied with a lot of force - this is not what's determining the degree of activity in the motor cortex Its rather the more precise movement, even if its applied with less force

Question 30

how does this relate to cases where there are motor lesions? | this being pinch grip and power grip study

Answer 30

Reflected in cases where theres damage to the motor cortex - typically don’t see an affect on these coarse actions with brute force like a power grip. But they rather seem to affect the fine motor controls Motor lesions result in loss of individuated use of fingers

Question 31

summarise the primary motor cortex

Answer 31

* The primary motor cortex, or M1, is one of the principal brain areas involved in motor function. M1 is located in the frontal lobe of the brain * Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells * Betz cells send long axons down the spinal cord to synapse directly onto the alpha motor neurons in the spinal cord which connect to the muscles * Somatotopic contralateral representation, although far more integrated * Size is based on precision/fine motor control rather than size of body part * Unclear specifically what the M1 codes, but individual muscles and complex actions can be 'stimulated'. In effect, it sends the signals required for movement * Motor cortical stroke: permanent loss of fine motor control

Question 32

where and what are frontal eye fields?

Answer 32

a region in the frontal lobe proposed that its kind of equivalent to the primary motor cortex, but for controlling eye movements seems to have a bit more complex cognitive functions than the primary motor cortex It really seems critical for the volitional control for eye movements, both in non-human primates and in humans Heavily connected to regions in the occipital lobe and superior colliculus So in the visual cortex, it receives a lot of bottom up input about visual surroundings can be activated sort of like bottom up by salient input and trigger reflexive eye movements - also heavily connected to regions in prefrontal cortex

Question 33

where and what is superior colliculus?

Answer 33

The activity in the superior colliculus is what initiates eye movements or eye muscle contractions So the circuit of the superior colliculus to the eye muscles is evolutionarily very old, and this is what's really allowing for very rapid reflex of eye movements to occur If something really really salient happens in your environment and you need to orient your attention extremely quickly - this is immediately mediated via the superior colliculus The frontal eye fields are this key circuit, these connections between the front eye fields and the superior colliculus is what ultimately allows you to modulate these involuntary responses

Question 34

what are secondary motor / association areas?

Answer 34

these areas are not directly controlling movement but they're really key to the whole process of motor control really important in selecting which motor programs in a given situation and kind of planning and sequencing them

Question 35

what are the 3 secondary motor areas?

Answer 35

* Supplementary motor area (SMA) * Pre-motor (PMC) ○ Dorsal PM (PMd) ○ Ventral PM (PMv) * Posterior parietal cortex *reference notes for locations

Question 36

how do secondary areas work?

Answer 36

* Very dense connections between secondary motor areas * Heavily connected to primary cortex - leading to execution of actions * SMA & PMC more involved in planning movements * Brain imaging shows activations when imagining or planning sequence of movements, even if no action is performed These secondary areas become active before movements are executed

Question 37

what is the posterior parietal cortex (PPC)?

Answer 37

* Links frontal cortex (decision-making) with premotor (planning) areas * Receives information from sensory regions (visual cortex, sensorimotor cortex etc.) * Important for determining potential actions/goals given the environment (pick up coffee, pick up sandwich, continue working) * Frontal cortex more critical in decision about which action to perform, and secondary area: develop plan for that action

Question 38

what is the supplementary motor area (SMA)?

Answer 38

SMA now considered to be two areas * SMA proper (motor learning) * Pre-SMA (motor execution) Postural stability Planning & executing complex sequential movements Initiation of internally generated movements (rather than stimulus driven)

Question 39

what is the dorsal premotor (PMd)?

Answer 39

Important in preparation of movement Learning conditional actions (response to external cues) * Red traffic light : foot on brake * Green traffic light : foot on accelerator * Set related activity - (' get ready, set, go')

Question 40

what was reported in the ventral premotor cortex (PMv)?

Answer 40

* First reported in ventral premotor cortex (PMv) * MNs show similar activity when monkey makes a goal directed action and when the same action is observed (visual), or heard (ripping paper) * Thought to be important for learning through observation * Also for understanding other people's intentions

Question 41

what is neuroplasticity?

Answer 41

The ability of the brain to form and reorganize synaptic connections, especially in response to learning or experience or following injury This can occur in all areas of the brain but there are very clear examples for the somatotopic maps in S1 and M1… Very pronounced in childhood and early development and decreases as you get older

Question 42

what is sensory remapping and what occurs during it?

Answer 42

Rapid changes in somatosensory (or motor maps) evident after change in inputs For example, when you learn a new skill such as playing the piano, the representations controlling your fingers might change and occupy more space Also in the context of injury, for example amputation, when there's complete lack of input and feedback signals from a particular body part Training ++ (pianist) Denervation - (amputation)

Question 43

what are the three conditions for sensory remapping?

Answer 43

training - expands the map denervation or amputation - reduces the map co-activation (surgically fusing two digits) - fuses the map

Question 44

how do changes in maps reflect neuroplasticity?

Answer 44

* Long term changes in functional connectivity e.g. growth of neurons * Branching (or pruning) of dendritic connections * Neurons appear to "compete" for space in the cortex - unused cortex gets taken over by other inputs * Imaging of the living mouse brain shows changes (growth & pruning) in dendritic branches in the mouse within hours or days of a new task

Question 45

what is a synapse?

Answer 45

enables one neuron to communicate with another

Question 46

what occurs in the pre-synaptic area?

Answer 46

increases vesicle volume increase availability of vesicles increase release probability

Question 47

what occurs in the synaptic cleft?

Answer 47

reduce re-uptake mechanisms reduce gap dimensions

Question 48

what occurs in the post synaptic region?

Answer 48

increase receptor density/area growth occurs, makes new synapses

Question 49

what is long-term synaptic plasticity?

Answer 49

Specific timed patterns of neuronal activity (or artificial simulation) can lead to long-term synaptic changes

Question 50

what is LTP, long-term potentiation?

Answer 50

is an activity-dependent persistent strengthening of synapses These produce a long-lasting increase in signal transmission between two neurons

Question 51

what is LTD, long-term depression?

Answer 51

is an activity-dependent reduction in the efficacy of neuronal synapses These produce a long-lasting decreases in signal transmission between two neurons

Question 52

how does associative LTP induction occur?

Answer 52

* NMDA channel is normally blocked by Mg++ * Concurrent voltage change to drive out Mg ++ - Achieved by glutamate binding to nearby AMPA receptors - Equivalent to stimulation with high frequency electrical pulses · Glutamate binds to NMDA & AMPA receptors - Temporary change in shape of channel, opens up channel - Calcium can enter through the open, unblocked NMDA channel · Ca++ entry triggers intra-cellular signalling cascade which results in - Migration of AMPA receptors from intracellular stores to the cell membrane - Synthesis of more AMPA receptors

Question 53

what is the key principle of LTP Cooperatively?

Answer 53

LTP requires simultaneous activation of large number of axons (due to large depolarisation)

Question 54

what is the key principle of LTP Associative?

Answer 54

When weak synaptic input is paired with strong, then large depolarisation can propagate and cause LTP at synapse with weak input

Question 55

what is the key principle of LTP Synapse specific?

Answer 55

If particular synapse is not activated then LTP will not occur even with strong post synaptic depolarisation

Question 58

what is the importance of synapse specific to learning and memory?

Answer 58

inputs that convey info not related to a particular event will not be strengthened to participate in a given memory

Question 59

is LTD related to learning?

Answer 59

* First identified in hippocampus, thought to be major component of motor learning in the cerebellum. * Cerebellar LTD involves a decrease in AMPA receptors. However, this is not NMDA-dependent.

Question 60

what is TMS?

Answer 60

Non-invasive measuring techniques - transcranial magnetic stimulation This is something where we can take advantage of the smarter topic representation of body parts Place a coil on the scalp, then you can deliver a brief pulse that causes electrical stimulation of the underlying neurone