Abnormalities of attention occur in humans for many psychiatric disorders, stroke or trauma-related injury to the frontal brain regions. Patients with these attention deficits often have difficulties concentrating, are easily distracted, and fail to notice relevant aspects of their environment, while they are unable to suppress irrelevant ones (known as response inhibition). Currently the brain mechanism of these attention deficits is poorly understood and thus difficult to treat. There is evidence, however, that the prefrontal cortex (PFC) is important for both the direction of attention and for the selection of appropriate actions. My long–term research goals are to develop a better understanding of the PFC modulation of the oculomotor system through the examination of how eye position, preparatory set signals and visual motion signals are modulated during various tasks (e.g. anti-saccade and delayed-match-to-sample). To this end, I have adopted a two-pronged research program utilizing both functional magnetic resonance imaging (fMRI) and single-unit electrophysiological techniques to address the many questions surrounding the oculomotor system and its relationship to attention. This dual approach is an effective and complimentary way to elucidate the neural mechanisms of the PFC and its relationship to attention and response inhibition.
During my training, I sought to understand the ways in which eye position signals modulate cortical activation sites in humans using fMRI. I systematically examined three cortical networks of the brain that control saccadic eye movements, hand and arm movements (DeSouza et al. 2000), and motion-related systems (DeSouza et al. 2002). I examined these networks as I manipulated the location at which the subjects maintained fixation in order to keep the view seen by the eye as identical. These results demonstrated for the first time that eye position signals are indeed used as an input signal to initiate multiple coordinate transformations within the human brain. In addition to gaining expertise in conducting fMRI experiments, I was a key member of the first team dedicated to the design and implementation of the fMRI research program. The only high field MRI facility, 4T, at the J.P. Robarts Research Institute, I participated in the early stages of all aspects of experimental design, custom equipment design, data acquisition, and pre-processing/analysis software development for our entire imaging group.
I pursued expertise in single-unit electrophysiology in order to more directly measure the neural activity since fMRI is only an indirect measure of neural activity. More specifically, I examined the role of the PFC neurons in attentional selection and response inhibition during the anti-saccade task (DeSouza and Everling 2004; Everling and DeSouza 2005). At the same time, I conducted fMRI studies where worked on anti-saccade preparatory signals (DeSouza et al. 2003) and memory guided eye movements (Brown et al. 2004). More recently, a collaborative project with Doug Crawford was highlighted on the main York webpagewww.yorku.ca/mediar/archive/Release.asp?Release=1191.
The objective of my future research program will be to continue to examine eye and hand position signals and examine frontal cortical attentional mechanisms involved in vision and action. For more information see www.joeLAB.com/.