7.6

• Somatosensory signals are ultimately conducted to the highest level of the sensory hierarchy, to areas of association cortex in prefrontal and posterior parietal cortex.
• neurons that respond to activation of two different sensory systems

  bimodal neurons
• inability to recognize objects by touch

  Astereognosia
• The failure to recognize parts of one’s own body.

  Asomatognosia
• Asomatognosia usually unilateral, only the left side of the body.
• Asomatognosia is usually associated with extensive damage to the right temporal and posterior parietal lobe
• The failure of neuropsychological patients to recognize their own symptoms.

  Anosognosia
• the tendency not to respond to stimuli that are contralateral to a right-hemisphere injury

  contralateral neglect
• The feeling that an extraneous object, in this case a rubber hand, is actually part of one’s own body.

  rubber-hand illusion
• Association cortex in the posterior parietal and frontal lobes plays a role in the rubber-hand illusion's induction.
• Frontal and parietal-bimodal neurons with both visual and somatosensory fields play a critical role in rubber-hand illusion.
• The perception of pain is paradoxical in three important respects:

  1. Pain is adaptive.
  2. Pain has no clear cortical representation.
  3. Pain is modulated by cognition and emotion.
• Painful stimuli activate many areas of cortex including the thalamus, SI and SII, the insula, and the anterior cingulate cortex.
• The cortical area that has been most frequently linked to pain is the anterior cingulate cortex.
• Pain is perceived when one’s hand is placed on a grid of metal rods that alternate between cool and warm.

  thermal grid illusion
• True or False, people injured in life-threatening situations frequently feel no pain until the threat is over.

  True
• Three discoveries led to the identification of a descending pain-control circuit:

  1. discovery that electrical stimulation of the periaqueductal gray (PAG) has analgesic (pain-blocking) effects
  2. the PAG and other areas of the brain contain specialized receptors for opioid analgesic drugs such as morphine
  3. isolation of several endogenous (internally produced) opioid analgesics, the endorphins
• Severe chronic pain in the absence of a recognizable pain stimulus.

  Neuropathic pain
• Although neuropathic pain may be perceived to be in a limb — it is caused by abnormal activity in the CNS.
• True or False, cutting nerves from the perceived location of the pain often brings comfort to a patient who experiences neuropathic pain.

  False