Neural Mechanisms for Visual-Motor Integration
Neuroprosthetics. One project in the lab is to develop a cognitive-based neural prosthesis for paralyzed patients. This prosthetic system is designed to record the electrical activity of nerve cells in the posterior parietal cortex of paralyzed patients, interpret the patients’ intentions from these neural signals using computer algorithms, and convert the “decoded” plans into electrical control signals to operate external devices such as a robot arm or a computer tablet.
Decision making. There are two influential theories of decision making. The goods-based model proposes that decisions are made in an abstract form by weighing the desirability of potential rewards and only then is an action planned to obtain the chosen object. The action-based model proposes that several potential plans are formed and that competition between these plans selects for the final decided action. These two theories are not mutually exclusive and our research examines action-based decision making in the posterior parietal cortex and how it connects to goods-based selection mechanisms.
Coordinate frames. Our laboratory examines the coordinate frames of spatial maps in cortical areas of the parietal cortex coding movement intentions. We have discovered that plans to reach are initially coded in the coordinates of the eye. This is a particularly interesting finding because it means the reach plan at this stage is still rather primitive, coding the plan in a visual coordinate frame rather than the fine details of torques and forces for making the movement. We have also been examining the coordination of eye and hand movements. In the dorsal premotor cortex we find a novel, “relative” coordinate frame is used for eye-hand coordination. Neurons in this cortical area encode the position of the eye to the target, the position of the hand to the target, and the relative position of the hand to the eye. A similar relative coding may be used for other tasks which involve the movements of multiple body parts such as bimanual movements.
Local field potentials. The cortical local field potential (LFP) is a summation signal of excitatory and inhibitory dendritic potentials that has recently become of increasing interest. We found that LFP signals in the saccade and reach regions provide information about the direction of planned movements as well as the state of the animal; e.g. baseline, planning a saccade, planning a reach, executing a saccade, or executing a reach. This new evidence provides further support for a role of the parietal cortex in movement planning. It also shows that LFPs can be used for neural prosthetics applications. Since LFP recordings from implanted arrays of electrodes are more robust and do not degrade as much with time compared to single cell recordings, this application is of enormous practical importance.
fMRI in non-human primates. We have successfully performed functional magnetic resonance imaging (fMRI) experiments in awake, behaving non-human primates. This development is important since this type of experiment is done routinely in humans and monitors the changes in blood flow during different cognitive and motor tasks. However, a direct correlation of neural activity with blood flow cannot be achieved in humans, but can in non-human primates. Thus, the correlation of cellular recording and functional MRI activation in non-human primates provides us with a better understanding of the many experiments currently being performed in humans. We are also using this magnetic resonance imaging, combined with neural recordings and reversible inactivation of brain areas, to examine the global structure of brain activity and its compensation for perturbations to sensorimotor circuits.