Deciphering Cortical Electrophysiological Signals and their Applications for Brain-Body Interfaces
|Cortical Dynamics, Cortical Maps, and the Hemo-Neural Hypothesis: Implications for Neural Prostheses
Christopher Moore, PhD; MIT
Brain-Computer Interfaces and Restorative Neurotechnology
The kick-off event of the Summer Education Series drew a capacity audience at the MIT McGovern Institute for Brain Research on July 10, and provided listeners with reasons for optimism regarding the future of restorative neurotechnology.
The series is part of the ongoing CIMIT Forum. This event marked the first of a four-part series in July titled: “Neurotechnology: Translating Basic Discoveries into Clinical Promise.”
Presenters were Christopher Moore, PhD, Mitsui CD Chair, assistant professor of neuroscience, Department of Brain and Cognitive Sciences, MIT; and Leigh Hochberg, MD, PhD, associate investigator, Department of Veterans Affairs, Providence (R.I.) VA Medical Center; investigator in neuroscience at Brown University, collaborating with the laboratory of John Donoghue; and instructor of neurology at Harvard Medical School, Massachusetts General Hospital.
Dr. Hochberg addressed the theme of “Brain-computer interfaces, restorative neurotechnology.”
He cited a small FDA-approved pilot study examining the feasibility of persons with tetraplegia controlling a computer cursor by imagining movement of their own hand.
Dr. Hochberg said that by harnessing the power of intracortically-recorded signals from motor cortex, neuronal activities are transmitted via cabling to a computer, and then decoded in real time into either the movement of a cursor or control over other external devices.
He presented video footage of a patient, with an attachment in his cranium, manipulating a cursor just by “willing it” to move. This function enabled him to open his email. The patient also was able to make a prosthetic hand open and close.
“Preliminary results have been encouraging,” said Dr. Hochberg, “There is potential for this and related neurotechnologies to re-enable the communication, mobility and independence of persons with a physical disability.”
He said that more than 100,000 worldwide are affected by serious immobility, and that such investigation has the potential to aid many patients.
Dr. Moore spoke on the subject of “Cortical Maps: New Hypotheses as to Their Computational Value and How They Might Save Neural Prosthetics.”
He suggested that changes in blood flow as it relates to neural activity could be a key factor in understanding brain-body interfaces.
If scientists are to create neural prostheses that will help tetraplegics interact with the world around them, it is critical that they understand the dynamics and organization of the cerebral cortex. In higher vertebrates, sensory areas of the cortex are often organized according to “feature” maps, in which spatially adjacent neurons perform similar functions. In the human visual cortex, for example, different patches of cells process different pieces of information, and these patches overlap to form distinct patterns, with individual neurons carrying out multiple tasks.
Cortical function is often studied using model organisms, such as the rat. Much of a rat’s sensory information is obtained not through vision but through its whiskers, or vibrissae. Neurons in the rat’s sensory cortex perform at least three different functions and are part of at least three different “feature” maps. First, information from each vibrissa is processed in a specific column, or “barrel,” of the cortex. Second, on the snout and in the cortex, vibrissae and their corresponding neurons are arranged according to vibrissa length, which determines a vibrissa’s resonant frequency. Finally, each “barrel” of neurons in the cortex is organized so that cells sensitive to movement in a particular direction are grouped together.
These observations raise an obvious question: why do we observe these broad patterns? Randomly positioned neurons could accomplish the same tasks. One hypothesis to explain the existence of these cortical maps suggests that neurons are grouped according to function so that they can be regulated by modulators on a multi-neuronal level.
Neuroscientists have traditionally believed that neurons do all the brain’s information processing, but Christopher Moore’s group has put forth what it calls the “hemo-neural hypothesis,” which posits that blood flow plays an active role in information processing. Although more work remains to be done, Moore’s group has shown that blood flow is spatially and temporally precise enough to potentially modulate brain activity.
Current knowledge about cortical maps suggests that developers of neural prostheses should be optimistic. Instead of measuring signals from individual neurons, they might be able to measure signals from patches of neurons. The hemo-neural hypothesis also implies that the recovery of the central nervous system after an injury could be aided by targeting the recovery of the brain’s circulatory system.
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