The Great Divide: Right and Left Hemispheres


1)     Holistic or Analytical

a)     Left brain: analytical, logical, precise, and time-sensitive

b)    Right brain: processes holistically rather than breaking things down into parts, more involved in sensory perception than abstract thinking.  More emotional than the left.  Cf. patient responses to right brain damage as compared to left.

2)     White and grey matter: cell bodies and bundles of axon

a)     The right brain has more white matter, left more grey:

i)       Right’s longer axons means left-brain connections to neurons that are farther away – broad, multifaceted thinking, vaguer.

ii)     Left brain draws on more brain modules at the same time – densely woven, more intense and detailed thinking

b)    Like An old married couple: one takes the dominant role, executive, day to day business most of the time, the other uses his/her particular talents to sense of the environment.  One keeps the other informed.

c)     What registers in one hemisphere registers in the other, but less fully.

3)     Incomplete hemispheric communications result in experiences of half knowledge:

a)     “Something awful has happened but it hasn’t hit me yet” (left brain acknowledges something but right hasn’t taken it in)

b)    “There’s something I don’t like about this but I can’t put my finger on it” (left brain (right brain grasps but left is only faintly aware)

c)     Rationalizing our actions: left brain processes that covers for the fact that our decisions were motivated largely by the emotional right brain

4)     Splitting the Brain

a)     Severing the connections by severing the corpus callosum and the anterior commissure (which connects the subcortical regions of the brain known as the limbic system)

i)       Normally, conscious stimuli is sent down from the cortex to the limbic system, evokes a response if significant (fear, anger), fed back to the cerebral hemispheres where it is processed into complex feelings.

b)    In split-brain patients, the normal and sophisticated processing back and forth is stopped. Twin-towered building connected only by an underground walkway (the anterior commissure).

i)       The case of V.P.: pp. 42, pp. 47-48  Passing of emotional stimuli between hemispheres is blocked in split brain patients.

ii)     Alien hands: in patients who have suffered damage to one or both brain areas, in split-brain patients.  Living in two minds.  Left brain may not always wrest physical control by passing inhibitory messages. pp. 48, 49