Lecture 6 = cerebral cortex

Question 1

Stroke

Answer 1

• Motor cortex dysfunctional
• Blockage or bleeding of vessels feeding brain
• Numbness = somatosensory cortex
• Weakness = primary motor cortex
• Brain organised somatotopiclly (by body part) = depending on where you have stroke, impacts what symptoms are

Question 2

What makes cortex unique in humans

Answer 2

• Heavily folder compared to other animals
• Larger number of cells making up brain
• Takes up less space than other animals because other areas of brain have developed

Question 3

Organisation of cerebral cortex

Answer 3

• 6 distinct layers = laminae (can vary in size and regions)
• Interconnecting to each other and other brain areas
• ytoarchitectural differences (cytoarchitectonics) define different areas
• Brodmanns areas = classification that allows us to describe which part of brain we are talking about = he went through layers of brain and decided where structure changed = found 52 areas of brain
• Since found can sub divide areas = not limited to 52

Question 4

Coritcal projections

Answer 4

• Betz cells = large pyramidal cells
• Project from motor cortex to spinal tract (cortical tract neurones)
• 5% project to motor-neurons = the rest reach spinal interneurons
• Most go to brain stem or interneurons (control circuits in spinal chord)
• Very few project to neurons that cause muscle to contract

Question 5

Mapping the motor cortex

Answer 5

• 1870= electrical stimulation of motor area = produced movement
• 1940 = surgery on epileptic patients = produced descriptions of how electrical stimulation causes movement in different parts of body = somatotopic map:
• -> Lower limbs = represented more medially in centre of brain

Question 6

Cortical motor maps

Answer 6

• Mirror relationship between sensory and motor map
• Proportional to amount of muscular control you have
• Neurons in motor and sensory cortex are related = have overlapping fields = enables muscles to be coordinated and enables complex movements

Question 7

What is represented in the motor cortex: muscles or movements?

Answer 7

• Brief micro-stimulation (50ms) = simple movement/contractions of contralateral muscles
• Prolonged stimulation = complex goal-directed actions
• Recordings from betz neurones for precision grip = strong association between force applied and electrical recordings = as involves fine degraded motor control
• Power grip (take whole hand and squeeze) = betz cells not interested in amount of force applied = involves whole hand contraction

Question 8

Primary motor cortex

Answer 8

• Codes for muscle forces and dynamic change in forces during voluntary movement
• Outputs connect to functionally related groups of muscles
• 5% of output directly connects to spinal motor-neurons
• Large % of output to brainstem and red nucleus
• Mostly makes indirect connections to motor-neurons via brainstem and spinal interneurons
• Fine control and “fractionation” of muscle activity
• Motor cortical stroke: permanent loss of dexterity (skill in performing task with hands)

Question 9

Frontal eye fields

Answer 9

• When stimulated causes eye movement
• Where you saccade depends where you stimulate in frontal eye fields
• If get flash of light = gets sent to superior colliculus = causes saccade
• Colliculus involved in voluntary and reflex eye movement = receives info from LGN directly and frontal eye fields

Question 10

Secondary motor/association areas

Answer 10

• Supplementary motor area (SMA)
• Pre-motor areas:
• -> Dorsal PM
• -> Ventral PM
• Posterior parietal cortex in between visual areas in occipital lobe and somatosensory in motor area
• Dense connection
• Connected to primary cortex= leading to execution of actions
• But SMA and PMC more involved in planning movements
• Object representation in parietal cortex, motor planning in the premotor areas and motor execution in motor cortex
• Activation of areas not only during movement, but when thinking about movements
• Supplementary motor area (SMA) now considered to be 2 areas:
• -> SMA proper (learning)
• -> Pre-SMA (execution)

Question 11

Pre-motor areas

Answer 11

• Dorsal PM = important in preparation of movement and learning conditional actions
• Ventral PM = important for sensory guidance of movement, responses to tactile, visual, auditory stimuli, language, Brocca’s area

Question 12

Mirror neurons

Answer 12

• Part of ventral PM
• Activated when you watch someone else perform an action
• First reported in ventral premotor cortex
• Doesn’t have to be visual, can be auditory
• Fed by visual, auditory system
• Producing and representing action rather than a simple movement