LATERALIZATION OF THE BRAIN cerebral commissures corpus callosum commissurotomy lateralization of function split brain aphasia apraxia Marc Dax Paul Broca Broca s area sodium amytal test dichotic listening test functional brain imaging Myer and Sperry experiment dextral and sinestral sex differences in lateralization differences between right and left hemispheres right hemisphere functions left hemisphere functions cross cuing helping hand phenomenon visual completion chimeric figure and test Z lens evolution of lateralization analytic synthetic theory motor theory linguistic theory 1 Introduction hemispheres communicate a How much of our abilities are lateralized in terms of our various abilities How do the b Seems seamless but we are seeing hearing from two different halves so does it impact you to have one side stronger i Left brain are more analytical organized math ii Right brained are more artistic musically inclines c Scientifically it is not so clear cut We cannot categorize people into such groups even if there are differences and tendencies to lean a certain way i One side of the brain can be more developed which may then cause the difference is performance 2 Cerebral Lateralization of Function a Discoveries i Marc Dax 1836 was first to report left hemisphere involvement in speech disorders caused by brain damage 1 Was treating patients that had suffered strokes and if they surfed aphasia speech disorder the left hemisphere was always involved no evidence of damage to the right hemispheres upon autopsy of the brains after death ii Paul Broca 1860 s was unaware of Dax s wok and made key discoveries in regarding left hemisphere involvement in aphasia 1 Same discovery but now attention given to it 2 A particular area of the brain is then labeled Broca s area as a result very small area a Damage that we see in individuals who suffer Broca s aphasia is not limited to the small area called Broca s area does not produce full extend of the speech problems if just Broca s is damaged i Now damage thought to be larger then originally thought to cause full range of issues b Characteristic symptoms of Broca s aphasia include labored and poorly articulated speech agrammatism telegraphic speech that is often pausing or halting anomia naming deficit where people have difficulty producing the names of objects or events situations and agraphia writing impairment as halting also 3 Region of brain damage is in the left inferior frontal cortex 3rd frontal gyrus anterior to the face in the region of the motor cortex called Broca s area iii Wernicke s Aphasia is another condition where we see damage in the temporal lobe 1 Characteristics include things in the left temporal lobe a Poor comprehension of spoke and written language b Fluent and spontaneous speech but incoherent sentences do not make sense are not grammatical c Paraphasia sound and word substitutions but in a way that they are senseless as sounds of different words are messed up and words are also mixed up with other words i Sound of words liked in ways that phonetically does not make sense almost as if they are talking in nonsense words that are non existent in the language d Alexia reading impairment 2 Region of the brain involved is the lest superior temporal gyrus with a portion tucked in over the edge of the gyrus into the fold of the temporal lobe called the Wernicke s area iv Both Brocas and Wernickes are only in the left hemisphere unilateral v Apraxia was identified by Hugo Karl Liepmann early 1900 s as the difficulty of movement on command 1 Difficulty performing movements with either side of the body when they are asked to do so but when do this spontaneously then they have no problem doing the same sort of movement only the specific asking makes the person have a hard time 2 This deficit is also located to damage in the left hemisphere of the brain vi Central lateralization of function there are differences between the functions of the left and right cerebral hemispheres 1 Cerebral commissures connect the two halves of the brain via projection fibers so that we normally do not have such problems in our lives as long as communication occurs between hemispheres a There are various connections in different locations the biggest of these is called the corpus callosum largest commissure i Transfers learned information from one hemisphere to another and when cut each hemisphere functions independently one hemisphere cannot pass sensory information coming in to the opposite side of the brain ii When each functions independently we see more evidence for lateralization as different behaviors occur in each side when there is no communication results in behavioral deficits b Tests of cerebral lateralization determining which hemisphere is dominant which hemisphere is in more primary control not that the other hemisphere will never take control of certain things i Sodium amytal test Wada test where the individual who is going to undergo some sort of neurosurgery goes in to get the brain mapped out in advance of the actual surgery to see if certain parts of the brain are more in control of certain functions 95 people have left hemisphere be dominant in speech but cortical function on brain mapped before surgeries to alleviate epilepsy 1 Anesthetize one hemisphere and check for language function as this is the main means of communication do not want to remove language from the patient 2 Sodium amytal is a radioactive label and is injected in carotid artery and only spreads out in the hemisphere on the side of the person in which it is injected person then asked to do things and we observe to see if behavior altered when one hemisphere put to sleep for a few seconds ii Dichotic listening test hear different digits sounds in each ear at the same time and then are asked to report what is heard tend to hear more items on the side of the dominant half 1 Monaural presentation would be when one sound given to one ear and the other thinks it hears it too due to the ipsilateral pathway 2 In dichotic presentation the ipsilateral pathway is suppressed and both ears will be presented with different noises so the more focused hemisphere dominant hemisphere will take over and you will hear one noise one side s stimuli more clearly a Most people have a left ear advantage LH for music and stimuli with a tonal quality musical scales and melodies b Right ear LH advantage for a verbal stimuli stuff that sounds like speech iii Functional brain