Lateralization and the Corpus Callosum We have contralateral control left controls right right controls left One sees some shared control and some same side control Ipsilateral means same side control Taste and odor and smell are ipsilateral control When light hits retina contralateral control makes sense Even though one has two hemispheres it is certainly the case that the two hemispheres talk to each other incredibly quickly 7 13 milliseconds Two hemispheres talk to each other primarily via the corpus callosum There is also an anterior commisure and the hippocampal commisure also help the hemispheres share information Two hemispheres are not mirror images of each other For most people left hemisphere is specialized for language One example of what is called a division of labor Division of labor is referred to as lateralization Damage to corpus callosum will interfere with sharing of information Every now and then someone has a severe case of epilepsy and the focal point of the epileptic seizure is close in the callosum So what surgeons do is cut the corpus callosum so the seizure can t bounce back and forth between hemispheres Individuals who have this kind of procedure done are called split brain patients There aren t many of them and they are studied to death Under normal circumstances these people function pretty well It s only when information is limited to one side of the body that one starts to see problems In the real world it doesn t happen but it does in a lab It doesn t take a whole lot of time before the anterior and hippocampal commisure take up some of the load of the corpus callosum so one only sees the real split brain early on in the lab They will sit people in front of a computer Flash word on the screen so only one side of the brain can see Something is flashed on left side of screen right side of brain sees it They re asked to reach behind a curtain feel around and pull out what they saw If they use their left hand they have no problems at all but if they have to use their right hand it s a guess because the information couldn t cross over Information is flashed to right side of the computer screen left hemisphere sees it Person can easily say what it was If something is flashed to left side of screen individual can t name it at all But if one allows them to use the left hand they can point to it The two hemispheres can and sometimes do operate independently Interestingly sometimes they can cooperate Right hemisphere is known in some circles as the original vice president It doesn t control speech or writing that s the left hemisphere It understands speech and the written word Right hemisphere controls emotional content of speech speech affect If one has right hemisphere damage they lack affect That s something one sees in individuals who suffer a right hemisphere stroke Right hemisphere is important for expressing emotion and hearing it Right hemisphere is more adept at recognizing and dealing with complex visual patterns It s important for spatial processing reading maps architectural design It s important for visual imagination Magnocellular cells are more important for overall pattern and movement parvocellular are important for detail Magnocellular cells are important in the right hemisphere Parvocellular are more important stronger in left hemisphere Left hemisphere is more sequential more analytic and more time dependent Most people when they listen to music are better able to identify tunes when they re played in left ear Professional musicians listen to music differently than the rest of us they re better at analyzing music in their right ears There are very subtle differences that one can see in people if one knows how to look When someone is putting together a crossword puzzle if one looks closely individuals look to the left There are a few anatomical differences between hemispheres There is one area in left hemisphere called the planum temporale that is larger in most people The difference is discernible to the naked eye It s an area that includes other areas important for language It s larger if one is more language developed The lateral fissure is larger than in the right hemisphere When one is born the corpus callosum is not fully developed It takes time The callosum completes its growth and development over the first 5 10 years of life It s not growing new axons but rather getting rid of the ones it doesn t need But it leads to interesting things in kids If callosum isn t completely developed then one might not get a complete transfer of information When dealing with things in both hands and comparing them older children did better than younger children There are times that a child may be born without a corpus callosum Most typically there s something else wrong with them Interestingly the child can function better than one would think That s because from the get go the anterior and hippocampal commisures take over the primary role of sharing information About 10 of population is left handed One doesn t see a reversal of hemispheral control One does see in most left handed people a larger corpus callosum because there s a little more bilateral control Also memory tends to be a little better because there s a lot of hemispheric sharing There s better explicit memory and episodic memory