6c. Somatosensory Cortex

Question 1

Primary Somatosensory Cortex

- Location

Answer 1

Post-central gyrus

Question 2

Primary Somatosensory Cortex

- Areas

Answer 2

3a = muscle stretch receptors in deep tissue

3b = slowly and rapidly adapting cutaneous mechanoreceptors

1 = rapidly adapting cutaneous mechanoreceptors

2 = pressure and join position in deep tissue

Question 3

Primary Somatosensory Cortex

- Horizontal Layers

Answer 3

6 layers

I-III:
Projects to:
- Ipsilateral SII
- Contralateral SI
- Posterior parietal cortex
- Motor cortex

IV:
Receives thalamic afferents

V:
Project to subordinate structures, including:
- Basal ganglia
- Brainstem
- Spinal cord

VI:
Projects tot eh thalamus

Question 4

Primary Somatosensory Cortex

- Vertical Columns

Answer 4

300-600micrometers wide
Span all 6 layers

Each column receives input from the same area of skin, preserving stimulus location

Each column receives neurones that respond to a single modality, preserving modality

Question 5

Directionally Sensitive Cortical Neurones

Answer 5

Only respond to stimulus movement in a particular direction

Allow shape reconstruction

Question 6

Context

Answer 6

Context can alter the responses of single inputs in SII

Context include:

• Attention
• Memory
• Interaction with motor system

Question 7

Context

- Attention

Answer 7

Attention enhances the responses of neurones in SII

Question 8

Context

- Memory

Answer 8

Responses from neurones in SII can reflect an animals memory

Question 9

Context

- Interaction with the Motor System

Answer 9

Passive touch activated:

• Area 3b of SI
• Area 1 of SI

Active touch activated:

• Area 3b of SI
• Area 1 of SI
• Area M1 (primary motor cortex)
• Anterior cingulate cortex (ACC)

Question 10

Active Touch

Answer 10

• Lateral motion = texture
• Pressure = hardness
• Static contact = temperature
• Unsupported holding = weight
• Enclosure = shape and volume
• Contour following = shape

Question 11

Cortical Plasticity

Answer 11

The cortex is plastic and cortical receptive fields can be modified by experience or injury.

Monkeys trained to maintain contact of digits 2-3 with a rotating disk in order to receive a reward developed a larger cortical representation of these digits.

Musicians have a larger cortical representation of the digits on their left hand compared to people who don’t play musical instruments

Question 12

Phantom Limb Sensation

Answer 12

Evidence for the theory of cortical remapping.

Cortical representation of the missing limb is altered, and in the case of arm amputation the cortical area previously mapping the hand is innervated by sensory neurones from the face and upper arm, whose cortical representations are adjascent to those of the missing arm. Therefore stimulating the face or upper arm generates sensation in the missing hand.

This is only true in 18-20% of phantom limb cases.

Studies have shown that the greater the reorganisation, the greater the phantom limb pain.

Question 13

Phantom Limb Sensation

- Another Example

Answer 13

Not limited to the somatosensory system:

- Tinistus is phantom auditory sensation.