Shelley Fried, PhD
Department of Neurosurgery/ Massachusetts General Hospital
Harvard Medical School
Boston Retinal Implant Project, Boston VA Healthcare System
Towards improved stimulation methods with neural prosthetics
In most neural prosthetic applications that target the CNS, the ability to create predictable and desirable patterns of neural activity remains limited. For example, the quality of visual percepts elicited by electric stimulation of the retina is directly correlated to the neural activity patterns elicited there, yet little is known about how retinal neurons respond to electric stimulation, or how to create specific patterns of neural activity. To gain insight about the mechanisms of activation, my lab uses a combination of electrophysiology, modeling and anatomical techniques to measure the response of single neurons to electric stimulation. This allows us to test the sensitivity of neurons to individual parameters of stimulation, e.g. pulse duration or frequency and also to study which features of neurons underlie responsiveness. Our most recent findings suggest that the use of previously untested sinusoidal waveforms may yield significant advantages over conventional pulsatile stimulation. For example, modulation of stimulus frequency allows preferential activation of different classes of neurons. In addition, the use of low frequency sinusoids avoids the activation of axons; this confines elicited activity to a ‘focal’ region around the stimulating electrode and provides for improved spatial accuracy. The implications of these findings for the development of a retinal prosthetic as well as for other CNS-based devices will be discussed.