How split is the split brain?
Some of my work on this topic has focused on vision. Each half of the visual world projects to the opposite hemisphere of the brain, and individuals who have undergone split-brain surgery, in which the corpus callosum connecting the two hemispheres is cut (usually for the relief of intractable epilepsy), generally show functional disconnection between the two sides of visual space. There are, however, some exceptions. Our research has shown some low-level visual interactions between the disconnected hemispheres and we explore their nature through the study of several split-brained patients in Italy. This provides insight into the role of subcortical structures in vision.
Cerebral asymmetry and handedness
The asymmetries in the way the human brain functions seem extraordinary in light of the overall bilateral symmetry of the human body. Cerebral asymmetry seems to underlie handedness, as evidenced by the fact that the vast majority of people show a preference for their right hand when performing most activities. We use magnetic resonance imaging to study how functional brain asymmetry relates to language, gestures, spatial attention, and the perception of faces. Our primary interests are whether these asymmetries are related, how they relate to handedness, and how they evolved in our species. Structural MRI reveals the anatomical asymmetries that underlie these functional asymmetries.
Cerebral asymmetry in twins
This project uses MRI to examine functional and structural asymmetries in twins. A particular focus of interest is on identical twins of opposite handedness (so-called “mirror twins”), who comprise some 22 percent of the population of identical twins. The question is whether they also show mirroring of various indices of cerebral asymmetry. This project is supported by a Marsden Fund grant, and is also providing general information about the interrelations between handedness and both structural and functional asymmetries.
Evolution of language
Arising from my interest in the connection between handedness and cerebral asymmetry for language, I have developed the idea that language evolved from manual gestures rather than from animal calls. This idea is supported by studies of the role of manual gestures in normal speech, by investigations of sign languages developed by deaf communities, by attempts to teach language to nonhuman primates, and by evidence that the homologues of the speech areas in nonhuman primates have to do with manual action rather than with vocalization. My current endeavour is to provide a plausible account of how the transition from manual gestures to spoken language might have occurred, based on the premise that speech itself is a gestural system rather than an acoustic one.
The human brain is continually active. In about half of our waking hours, our minds wander away from the present—into the past and future, into other places, into the minds of others. This depends on a network in the brain known as the “default mode network.” Although mind wandering can take us away from the task at hand, it is important in planning and creativity. Mind wandering is the basis of the human predilection for gossip, stories, fiction, and even religion.