Showing papers by "Michael S. Gazzaniga published in 2005"

Forty-five years of split-brain research and still going strong.

Abstract: Forty-five years ago, Roger Sperry, Joseph Bogen and I embarked on what are now known as the modern split-brain studies. These experiments opened up new frontiers in brain research and gave rise to much of what we know about hemispheric specialization and integration. The latest developments in split-brain research build on the groundwork laid by those early studies. Split-brain methodology, on its own and in conjunction with neuroimaging, has yielded insights into the remarkable regional specificity of the corpus callosum as well as into the integrative role of the callosum in the perception of causality and in our perception of an integrated sense of self.

Dissociating processes supporting causal perception and causal inference in the brain.

Abstract: An understanding of relations between causes and effects is essential for making sense of the dynamic physical world. It has been argued that this understanding of causality depends on both perceptual and inferential components. To investigate whether causal perception and causal inference rely on common or on distinct processes, the authors tested 2 callosotomy (split-brain) patients and a group of neurologically intact participants. The authors show that the direct perception of causality and the ability to infer causality depend on different hemispheres of the divided brain. This finding implies that understanding causality is not a unitary process and that causal perception and causal inference can proceed independently.

Functional Connectivity: Integrating Behavioral, Diffusion Tensor Imaging, and Functional Magnetic Resonance Imaging Data Sets

Abstract: & In the present study, we combined 2 types of magnetic resonance technology to explore individual differences on a task that required the recognition of objects presented from unusual viewpoints. This task was chosen based on previous work that has established the necessity of information transfer from the right parietal cortex to the left inferior cortex for its successful completion. We used reaction times (RTs) to localize regions of cortical activity in the superior parietal and inferior frontal regions (blood oxygen level-dependent [BOLD] response) that were more active with longer response times. These regions were then sampled, and their signal change used to predict individual differences in structural integrity of white matter in the corpus callosum (using diffusion tensor imaging). Results show that shorter RTs (and associated increases in BOLD response) are associated with increased organization in the splenium of the corpus callosum, whereas longer RTs are associated with increased organization in the genu. &

A Dissociation between the Representation of Tool-use Skills and Hand Dominance: Insights from Left- and Right-handed Callosotomy Patients

Abstract: & The overwhelming majority of evidence indicates that the left cerebral hemisphere of right-handed humans is dominant both for manual control and the representation of acquired skills, including tool use. It is, however, unclear whether these functions involve common or dissociable mechanisms. Here we demonstrate that the disconnected left hemispheres of both right- and left-handed split-brain patients are specialized for representing acquired tool-use skills. When required to pantomime actions associated with familiar tools (Experiment 2), both patients show a right-hand (left hemisphere) advantage in response to tool names, pictures, and actual objects. Accuracy decreases as stimuli become increasingly symbolic when using the left hand (right hemisphere). Tested in isolation with lateralized pictures (Experiment 3), each patient’s left hemisphere demonstrates a significant advantage over the right hemisphere for pantomiming tool-use actions with the contralateral hand. The fact that this asymmetry occurs even in a left-handed patient suggests that the left hemisphere specialization for representing praxis skills can be dissociated from mechanisms involved in hand dominance located in the right hemisphere. This effect is not attributable to differences at the conceptual level, as the left and right hemispheres are equally and highly competent at associating tools with observed pantomimes (Experiment 4). &

Localization of the Human Cortical Visual Area MT Based on Computer Aided Histological Analysis

Abstract: We describe human area MT histologically based on the observer independent analysis of cortical myeloarchiteture, multiple complementary staining techniques and 3-D reconstruction. The topography of an architectonic field that presented constant structural characteristics across specimens was studied in relation to the sulcal geography of the occipito-temporal region. Objective and semi-automated analysis of local microstructure revealed a distinct cortical architecture and matched topographically the localization of MT derived from functional imaging. MT was localized by the histotopographic method in relation to definite macroscopic landmarks. This study demonstrates a new set of distinguishing architectonic features of human MT that permit localization on structural grounds and suggests that the characteristic laminar structure of this area may be related to its unique pattern of connections and to its role in visual perception.

Can perceptual expertise account for the own-race bias in face recognition? A split-brain study

Abstract: The own-race bias (ORB) in facial recognition is characterised by increased accuracy in recognition of individuals from one's own racial group, relative to individuals from other racial groups. Here we report data from a split-brain patient indicating that the ORB may be tied to functions lateralised in the right cerebral hemisphere. Patient JW (a Caucasian) performed a delayed match-to-sample task for faces that varied both the race of the facial memoranda-Caucasian or Japanese-and the cerebral hemisphere performing the task. While JW's left hemisphere showed no effect of race on facial recognition, his right hemisphere demonstrated a significant performance advantage for Caucasian faces. These findings are discussed in relation to stimulus familiarity and the development of perceptual expertise.

Lateralization of language: Toward a biologically based model of language

Abstract: If the biological basis of language is to provide insight for linguistic theory, description of the aspects of language that play a role in the determination of language lateralization is essential. This article will summarize what is known about the distribution of language across the hemispheres using information from the Wada procedure and comparing those results with those from investigations using newer less invasive methods like fMRI. This article will also describe what is known about the limits of language in the isolated right hemisphere when acquired during normal language development. The profile of language in the isolated right hemisphere may qualify as one model of an evolutionarily older "protolanguage." Questions posed in both of these areas provide a rich opportunity for interaction between linguists, psycholinguists, and neuropsychologists.

Chapter 23 Blindsight: hypotheses and clinical implications

Abstract: Publisher Summary People who are partially blind due to brain damage or surgery that has compromised their visual system can occasionally respond to stimuli placed within their region of clinically defined blindness. This phenomenon has come to be called “blindsight” because the patients show “sight” where they are clinically “blind.” Blindsight, by its very nature, continues to be controversial. Their sight is not normal, in that, patients are often unaware of seeing anything presented within their blind field; however, they are often able to respond to stimuli presented within their blind field. This phenomenon—blindsight—has been operationally defined as “residual visual abilities within a field defect in the absence of acknowledged awareness.” This chapter discusses the history of blindsight, outlines the three prominent hypotheses regarding the neurobiological underpinnings of blindsight and describes research key to analyzing these hypotheses, and concludes with clinical implications concerning residual vision, blindsight and visual restitution.

Research report Brain mechanisms underlying perceptual causality

Abstract: Functional magnetic resonance imaging (fMRI) was used to examine the neural correlates of perceptual causality. Participants were imaged while viewing alternating blocks of causal events in which a ball collides with, and causes movement of another ball, versus non-causal events in which a spatial or a temporal gap precedes the movement of a second ball. There were significantly higher levels of relative activation in the right middle frontal gyrus and the right inferior parietal lobule for causal relative to non-causal events. Furthermore, when the differential effects of spatial and temporal incontiguities were subtracted from the contiguous stimuli, we observed both common (right prefrontal) and unique (right parietal and right temporal) regions of activation as a function of spatial and temporal processing of contiguity, respectively. Taken together, these data provide a means to help determine how the visual system extracts causality from dynamic visual information in the environment using spatial and temporal cues. D 2004 Elsevier B.V. All rights reserved. Theme: Neural basis of cognition Topic: Cognition

Attention in Split-Brain Patients

Abstract: Attention can take many different forms in human information processing, yet one question central to all domains of attention research concerns understanding how our attentional capacities are controlled. Accordingly, the study of attentional functioning in split-brain patients has long focused on investigating the degree to which attention is independently controlled in the two cerebral hemispheres. In particular, severing the corpus callosum disrupts the ability of the two hemispheres to directly communicate, and as a result, the hemispheres can no longer coordinate their operations in a strategic and organized manner. As a result, each hemisphere in the split-brain patient is thus believed to function in a relatively independent manner, a condition that is ideal for examining the laterality of attentional control processes. For example, if a split-brain patient is given a visual search task to perform, at least three different results may be obtained, each of which is informative regarding the implementation of attentional control processes in cortex. If each hemisphere can independently search the display elements in the contralateral visual hemifield, it would suggest that the control processes mediating visual search exist in parallel within each hemisphere. Conversely, if only one of the two hemispheres shows an ability to perform visual search, it would support the proposal that control processes are lateralized to that hemisphere. Finally, if the split-brain patient is unable to perform the visual search task, it would be consistent with the idea that attentional processes underlying visual search are distributed—or integrated—across the two cerebral hemispheres.