On 18 Sep 2003, jpuente wrote: > I have an interesting question posed by one of my students re: the > capabilities of a split brain patient. > > <snip> > The dilemna: > In a video demonstration, after seeing the word car in his left visual > field, a split brain patient was able to draw, with left hand, a > picture of a car. This demonstration implies that the right > hemisphere has the ability to allow a splitbrain person to understand > language (he read the word and drew a picture of it), but not provide > speaking capabilities. Does this mean that Wernicke's area is only > important for speach comprehension (not other language comprehension)? > And, if so, what other areas mediate language comprehension? >
Good question. I'd just suggest that it not be limited to Wernicke's area but phrased more generally: Does the right hemisphere have language ability, in particular the ability to read? There would be no problem if the patient had his speech represented in the right hemisphere. And yes, some people do have bilateral or right-hemisphere language representation, but these are mostly lefties, and they're still a minority. One recent fMRI imaging study (Pujol et al, 1999) found that 76% of left-handers had left-side only language representation and this figure went up to 96% in right- handers. On the other hand, split-brainers were split because of severe and long-standing brain dysfunction, which may have compromised the left hemisphere, promoting a shift to right- hemisphere representation of language. In fact, Springer et al (1999), in another fMRI study, found (in r-handers), that 94% of normals were left-dominant for language but only 78% of an epilepsy group. So the percentage of patients with right-side language representation is probably greater in split-brain cases than in normals. But the patient shown in the video may not have been one of these. So I checked textbooks. Carlson, in his 8th edition _Physiology of Behavior (2004), gives little space to split-brain, and says flatly that the right hemisphere can't read (p. 6). But other sources show that a standard testing technique is to present different words to the different hemispheres and observe different responses (as in the video). As not all of these people are likely to be right-hemisphere dominant for language, it suggests that the right hemisphere must be able to read and understand individual words. This is what Pinel, in _Biopsychology, 5th ed_ (2003) says: "In most split-brain patients, the left hemisphere is dominant for language, but the right hemisphere can understand many spoken or written words and simple sentences (see Baynes & Gazzaniga, 1997; Zaidel, 1987)...although there is considerable variability among split-brain patients in the performance of their right hemisphere on tests of language comprehension (Gazzaniga, 1998), the language abilities of their right hemispheres tend to be comparable to those of a preschool child" [but one who can read, apparently]. Just to be sure, I also tried Kandel, _Essentials of Neural Science_ (1995), and his take is similar. He says: "We speak after all, as Broca first illustrated, with our left hemisphere. Nevertheless, the right hemisphere may be capable of a primitive understanding of language. For example, some words projected to the right hemisphere can be read and understood. If the letters D-O-G are flashed in the left visual field (the right hemisphere) the patient selects a model of a dog with his left hand. More complicated verbal inputs to the right hemisphere, such as comands, are comprehended poorly. Although the right hemisphere appears almost totally incapable of language _output_, it does seem able to process simple linguistic _inputs_.": (p. 356) So it's another example that the left-right dichotomy (this side of the brain does this; that side does that) is too simple a description for what really is going on. Stephen Springer, J., and a bunch of others (1999). Language dominance in neurologically normal and epilepsy subjects: a functional MRI study. Brain, 122, 2033-46. Pujol, J. et al (1999). Cerebral lateralization of language in normal left-handed people studied by functional MRI. Neurology, 52, 1038-43. ______________________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Dept web page at http://www.ubishops.ca/ccc/div/soc/psy TIPS discussion list for psychology teachers at http://www.frostburg.edu/dept/psyc/southerly/tips _________________________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
