Biological Psychology – Module 4 The Split-Brain Phenomenon Synaptic Plasticity Intro Psych Feb 12-19, 2010 Classes #11-13

The Split-Brain Phenomenon Corpus Callosum Corpus Callosum Large band of neural fibers that connects the two brain hemispheres Large band of neural fibers that connects the two brain hemispheres The two sides of our brains serve different functions (lateralized or specialization of tasks): The two sides of our brains serve different functions (lateralized or specialization of tasks): Left hemisphere: Language, math, logic Left hemisphere: Language, math, logic Right hemisphere: spatial abilities, face recognition, visual imagery, musical and artistic abilities, emotional tasks. Right hemisphere: spatial abilities, face recognition, visual imagery, musical and artistic abilities, emotional tasks. This is the case for almost all righthanders (about 95%) and about half of lefthanders This is the case for almost all righthanders (about 95%) and about half of lefthanders

Important aspects of this divided brain phenomenon Information from left half of field of vision is received only by your right hemisphere, and information from the right half of your field of vision is received only by your left hemisphere Information from left half of field of vision is received only by your right hemisphere, and information from the right half of your field of vision is received only by your left hemisphere Don’t get confused here as each eye receives sensory information from both right and left visual fields. But this information is only transmitted from a particular visual field to a particular brain hemisphere Don’t get confused here as each eye receives sensory information from both right and left visual fields. But this information is only transmitted from a particular visual field to a particular brain hemisphere

Important aspects of this divided brain phenomenon The left hemisphere receives information from and controls movements of the right side of the body, whereas the right hemisphere receives input from and controls movements of the left side of the body The left hemisphere receives information from and controls movements of the right side of the body, whereas the right hemisphere receives input from and controls movements of the left side of the body Tests show that almost all right-handers (over 95%) process speech in the left hemisphere Tests show that almost all right-handers (over 95%) process speech in the left hemisphere

Important aspects of this divided brain phenomenon Left-handers are more diverse: Left-handers are more diverse: 60% process speech in the left hemisphere 60% process speech in the left hemisphere 5% process speech in the right hemisphere 5% process speech in the right hemisphere 35% use both hemispheres about equally (half of the time) 35% use both hemispheres about equally (half of the time)

Split-Brain Experiments Vogel and Bogen (1961) Vogel and Bogen (1961) Sperry and Gazzaniga Sperry and Gazzaniga Conducted many experiments from 1960’s through the 1980’s Conducted many experiments from 1960’s through the 1980’s

The Split-Brain Phenomenon FIELD OF VISION LEFT RIGHT HEMISPHERE LEFT RIGHT When the patient is asked “What do you see?” They answer …

The Split-Brain Phenomenon FIELD OF VISION LEFT RIGHT HEMISPHERE LEFT RIGHT When the patient is asked “What do you see?” They answer …

The Split-Brain Phenomenon FIELD OF VISIONLEF T RIGHT HEMISPHERE LEF T RIGHT The same patient who has just said they could not see the picture is now asked to take their left hand and touch the ‘happy face” picture… What happens now???

The Split-Brain Phenomenon FIELD OF VISIONLEF T RIGHT HEMISPHERE LEF T RIGHT Now, with the object in the patient’s hand, he/she is asked “what is in your hand”…what is their answer this time???

Severed Corpus Collusom: Video 1 st scene: 1 st scene: “Joe” is flashed words in his right field of vision (“storm” and “piano”) and has no trouble saying them “Joe” is flashed words in his right field of vision (“storm” and “piano”) and has no trouble saying them He is then flashed the word “phone” in the left field of vision…and he can’t say it He is then flashed the word “phone” in the left field of vision…and he can’t say it “didn’t see that” “didn’t see that” But when asked to draw a picture of what he saw with his left hand…he draws a telephone but since its still in his left field of vision he still can’t verbalize what he just drew But when asked to draw a picture of what he saw with his left hand…he draws a telephone but since its still in his left field of vision he still can’t verbalize what he just drew

Severed Corpus Callosum: Video But then when asked to draw it with his left hand but in his right field of vision…he is able to say what he drew (“oh, phone”) But then when asked to draw it with his left hand but in his right field of vision…he is able to say what he drew (“oh, phone”) Very interesting… Very interesting…

Severed Corpus Collusom: Video 2 nd scene: 2 nd scene: Joe is flashed words simultaneously in both fields of vision – “toad” in left field and “stool” in right field… Joe is flashed words simultaneously in both fields of vision – “toad” in left field and “stool” in right field… He can’t say “toad” but can draw it with left hand He can’t say “toad” but can draw it with left hand He can say ‘stool” and by speaking it, he is able to let the right hemisphere in on the “secret” He can say ‘stool” and by speaking it, he is able to let the right hemisphere in on the “secret”

Severed Corpus Collusom: Video 3 rd scene: 3 rd scene: Again, two words simultaneously…”bell” appears in his left field of vision and “music” in his right field of vision Again, two words simultaneously…”bell” appears in his left field of vision and “music” in his right field of vision When asked to point with his left hand to what he saw, Joe points to a picture of a bell but is not really sure why so he makes up a story that seems to be plausible…he’s basically trying to figure out what's going on When asked to point with his left hand to what he saw, Joe points to a picture of a bell but is not really sure why so he makes up a story that seems to be plausible…he’s basically trying to figure out what's going on

Severed Corpus Callosum : Video Joe’s left hemisphere is trying to interpret what is going on – trying to find a cause and effect Joe’s left hemisphere is trying to interpret what is going on – trying to find a cause and effect Left hemisphere is responsible for making sense out of the mystery Left hemisphere is responsible for making sense out of the mystery According to Gazzaniga: “the left hemisphere is where the action is”… According to Gazzaniga: “the left hemisphere is where the action is”…

Severed Corpus Callosum : Video Final scene: Final scene: Pictures are shown of faces made out of fruit, meat, etc. Pictures are shown of faces made out of fruit, meat, etc. Right hemisphere specializes in locating faces and left is better at finding elements involved… Right hemisphere specializes in locating faces and left is better at finding elements involved… So what happens? So what happens? Right hemisphere sees it as a face and left hemisphere sees it as a fruit Right hemisphere sees it as a face and left hemisphere sees it as a fruit

Still being performed but now very rare Cutting apart the two hemispheres of the human brain is a drastic step, and it is one of the most controversial operations ever performed Cutting apart the two hemispheres of the human brain is a drastic step, and it is one of the most controversial operations ever performed Yet it can succeed, when all else fails, in relieving violent, drug-resistant epileptic seizures Yet it can succeed, when all else fails, in relieving violent, drug-resistant epileptic seizures This surgery is becoming more and more rare – Instead, neurosurgeons are using a variety of neuroscience techniques to reduce the amount of tissue removed in brain surgery This surgery is becoming more and more rare – Instead, neurosurgeons are using a variety of neuroscience techniques to reduce the amount of tissue removed in brain surgery Hardly ever performed now because also because of new and effective medications that help prevent seizures Hardly ever performed now because also because of new and effective medications that help prevent seizures

Brain Reorganization: Synaptic Plasticity Synaptic Plasticity Synaptic Plasticity Often when one area of the brain is damaged, other areas may in time reorganize and take over its function Often when one area of the brain is damaged, other areas may in time reorganize and take over its function It is not uncommon for stroke patients who have lost the ability to speak or to move a limb to regain function after several weeks of convalescence It is not uncommon for stroke patients who have lost the ability to speak or to move a limb to regain function after several weeks of convalescence

How does the brain recover? Essentially what is occurring is a “remodeling” of the cerebral cortex after an injury in which sometimes a large part of it simply dies Essentially what is occurring is a “remodeling” of the cerebral cortex after an injury in which sometimes a large part of it simply dies Of course, this is the exception and not the rule Of course, this is the exception and not the rule Not all stroke victims recover Not all stroke victims recover

Even better chances: Plasticity in children Before the functions of young children’s cortical regions become fixed, their brains are especially plastic…if the speech areas of an infant’s left hemisphere are damaged, the right hemisphere will usually take over with no noticeable impairment of language… Before the functions of young children’s cortical regions become fixed, their brains are especially plastic…if the speech areas of an infant’s left hemisphere are damaged, the right hemisphere will usually take over with no noticeable impairment of language… Left hemisphere damage does not permanently disrupt language until age 8 Left hemisphere damage does not permanently disrupt language until age 8 Case study: see hand-out Case study: see hand-out Illustrates that the brain has extraordinary powers of reorganization, especially when damaged before it is fully developed Illustrates that the brain has extraordinary powers of reorganization, especially when damaged before it is fully developed