Showing papers by "Michael S. Gazzaniga published in 1993"

Three-Dimensional Quantitative Analysis of Hemispheric Asymmetry in the Human Superior Temporal Region

Abstract: The recent observations of overall symmetry of the caudal infrasylvian region by Steinmetz et al. (1990) and Witelson and Kigar (1991, 1992) diverge from earlier findings of leftward asymmetry in this region (Geschwind and Levitsky, 1968; Galaburda et al., 1987; Larsen et al., 1989). To address this inconsistency, we measured the entire infrasylvian surface posterior to Heschl's gyrus from coronal magnetic resonance images of 10 young, normal, right-handed subjects. Computer models were constructed by tracing contours of this region and then interpolating a 3D triangle mesh between each pair of adjacent contours. Measurements of these models showed no significant directional asymmetry. The same contour set was used to obtain measurements with a conventional algorithm that does not interpolate a surface between contours. The results obtained with the second method showed significant leftward asymmetry. These results suggest that in some cases, unbalanced distortions due to folding differences of the hemispheres are sufficient to obtain spurious findings of left-right asymmetry. This supports the claim of Steinmetz and Witelson that leftward asymmetry is restricted to the temporal bank of the caudal infrasylvian surface, and is balanced by rightward asymmetry of the parietal bank.

Brain mechanisms and conscious experience.

Abstract: The human brain enables a variety of unique mental capacities. Our special capacities for inference, personal insight into the reasons for our actions, deception, high level problem solving, for literally dozens of activities represent specialized systems that most likely reflect specialized neuronal circuits that have accumulated in our brain by selection processes over thousands of years of evolution. I believe many of these enriching capacities are not so much the advantageous computational products of a large neuropil as they are the product of a brain that has accumulated specific algorithms for adaptation. Our awareness, our consciousness of these capacities, is nothing more or less than a feeling about them. A correlate of this view is that there are many processes supporting human cognition of which we are neither aware nor conscious. When conscious appreciation or feeling is involved for a modality of sensation or action, neural pathways communicating this information must be intact, normally to the left hemisphere. This paper reviews evidence that supports this view of consciousness that distinguishes special human capacities and feelings about those capacities from the neural substrates that underlie these distinctions.