Touch and pain Chapter 8 (cont.)

Somatosensation includes a variety of submodalities Fine touch pain temperature kinesthesis joint position muscle stretch interoception

Somatosensation involves a variety of receptors

Transduction usually involves stretch

Input from different receptors is carried by different fibres

Receptor specificity is carried into spinal cord

Input from different parts of the body is segregated into dermatomes

Somatosensory input ascends to cortex Ventral posterolateral nucleus of the thalamus

Submodality processing in cortex

Columnar organization in cortex

Barrel fields in rat cortex

Somatosensory agnosias Astereognosia – can’t recognize objects with hands Anosognosia – deny neurological symptoms Asomatognosia- deny ownership of body parts Neglect – neglect of left half of body and external world in grooming, drawing, etc.

The man who mistook his wife for a hat: The opera?

Pain is multifaceted

Pain transduction is chemosensory

Central pain pathways

Central pain pathways II

Descending control of pain

Endogenous opiates and pain control

More complicated pain phenomena Phantom limb pain –Suggests that one can experience pain without a transduction event Chronic pain syndromes –Sometimes pain persists in the absence of any evidence of trauma

Phantom limb pain Feelings of pain, pressure, burning in missing limb Walls’ theory does not account for facts very well Melzack hypothesizes that there is a complex ‘neurosignature’ that composes the perception of self

Merzenich and neural plasticity Following amputation, considerable re- arrangement of neocortex takes place

Merzenich (cont)

Vilayanur Ramachandran rearrangement of sensory cortex is responsible for phantom limb pain

Functional imaging of somatosensory cortex in a right limb amputee (From Ramachandran, 2000)

Possible treatment for phantom limb pain? Mirror imaging of limbs