PSYCH 169: Lecture 6 (Week 3), The unity of consciousness, Split-brain patients, Alien hand syndrome, functional organization of the corpus callosum, hearing, touch, olfaction in split-brain patients

epilepsy

a debilitating disease that could cause seizures several times per day

corpus callosotomy

radical new surgery to cut the corpus callosum (untested in humans)

William Van Wagenen, Archives of Neurology and Psychiatry

-got the idea for corpus callosotomy from two seizure patients with small tumors on the corpus callosum

-the tumor grew, destroyed corpus callosum

-seizures eased up (no loss of consciousness)

corpus callosum

200 million nerve fibers (axons)

-cut to prevent seizures from spreading from one side of the brain to the other

callosum tissue appearance

the callosum tissue seeing in a healthy brain (bright white in top image) retracts after a corpus callosotomy, leaving just the ventricle (black)

What happens to IQ after cutting corpus callosum

-IQ remains the same

-what happens to their personality?

-same personality

-verbal and problem solving ability?

-same

-patients recover and live normal life

What actually changes in split-brain patients?

Roger Sperry (1913-1994)

-Caltech

-Nobel Prize (1981)

-information from the left visual field goes to the right hemisphere, and from the right visual field to the left hemisphere

the word "face" shows to the right side of split-brain patient

-because the left hemisphere is dominant for verbal processing, the patient's answer matches the word

the word "face" shows to the left side of split-brain patient

-the right hemisphere cannot share information with the left so the patient is unable to say what he say, but he can draw it

Roger Sperry

-split brain patient is two conscious people

-two free wills

-Is one of the two in charge?

"... the minor hemisphere constitutes a second conscious entity that is characteristically human and runs along in parallel with the more dominant stream of consciousness in the major hemisphere" (Sperry, 1968)

Michael Gazzaniga (UCSB)

-the left brain is the "interpreter"

-Right brain: points to shovel (snow)

-left brain interprets the action to fit a story

-Steven Pinker (Harvard): left brain is the baloney generator (makes up stories)

Steven Pinker (Harvard):

-left brain is the baloney generator (makes up stories)

"...spooky part is that we have no reason to think that the baloney-generator in the patient's left hemisphere is behaving any different from ours..."

"...the conscious mind is a spin doctor, not the commander in chief"

What about the right hemisphere? Is it conscious with a sense of self?

Gazzaniga: only the left hemisphere has high-level consciousness (language, beliefs)

Is the right hemisphere a Zombie?

-right hemisphere has:

-linguistic ability of a 3-year old child

-reasoning capacity of a chimpanzee

-is it conscious?

Donald Mackay

taught each hemisphere of a split-brain patient's brain to play a number guessing game with each other.

-is this evidence for two conscious systems?

alien hand syndrome (intermanual conflict)

-each hand acts on its own

-seen in split-brain patients, but also results from stroke, tumor, that damage the frontal lobe

-functional dissociation of thought and action

functional organization of the corpus callosum

-posterior regions

-anterior regions

-middle regions

posterior regions

transfer basic sensory information: vision, audition, somatosensory

anterior regions

transfer of attention and higher cognitive information

middle regions

motor functions

how do split-brain patients walk?

-left brain controls right leg, right hand, etc.

-soon after surgery, patients can walk, run, play piano, dance,...

-How is this possible?

cross cuing

non-neural interhemispheric communication in split-brain patients

-analogous to how conjoined twins may operate (two brains, one body)

-Abby and Brittany Hansel

Other ways in which the left and right brains may communicate in split-brain patients:

subcortical pathways (brainstem, cerebellum)

hearing, touch, and olfaction in split-brain patients

-split-brain patients: other senses?

-auditory (high-low-high tones to left ear)

-melodic pattern cannot be identified (speech)

-but can be "hummed" (motor system)

tactile

patient closes eyes, given object (apple) to left hand

-can't verbally identify

-can draw apple with left hand

Olfaction

-smell of garlic to right nostril

-olfactory receptors project ipsilaterally

-patient looks disgusted

-says: "I smell nothing"

-her left hand pointed to correct object (garlic)