Anticipatory Hemodynamic Signals in Primary Visual Cortex

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PROJECT SUMMARY The long-term goal of the lab is to understand the neural mechanisms of visual processing early in the cortical pathway. To this end the lab records from rhesus macaque visual cortex using a combination of intrinsic-signal optical imaging and electrophysiology while the animals perform visual tasks. This project derives from earlier work showing that V1 (primary visual cortex) imaging signals in alert, task- engaged macaques have two components. One component is related to stimulation and V1 neuronal activity. The other component - of comparable strength - is a novel task-related signal independent of local spiking. Later work showed that when the animal performs stereotyped tasks, the task-related signal can be removed linearly from stimulus-evoked signals which can then be related with particularly high reliability (>90%) to local spiking. The task-related signal, on the other hand, is strongly modulated by factors such as reward size, task structure and performance, suggesting its role as a form of arousal or attention independent of local spiking. These results were obtained using the support of my last grant. The current proposal is a resubmission of my request for a competitive renewal of the same grant. This current project has two goals that derive from the above observations. The first goal is to generalize the observed link between stimulus-evoked imaging and spiking, as a broad principle for interpreting brain images. This would be valuable for the interpretation of fMRI, one of the most widely used neuroscience research tools. The second goal is to define the factors controlling the task-related signal and the effect of this signal on performance. This goal is expected to provide insights about a novel brain mechanism of attention or arousal, as well as the etiology of attentional disorders such as ADD and ADHD. The novel findings at the base of this proposal were obtained as a result of an imaging technique developed in our laboratory, continuous dual-wavelength intrinsic-signal optical imaging, combined with electrode recordings, in alert behaving macaques. For the imaging, one wavelength, absorbed preferentially in oxygenated hemoglobin, monitors blood oxygenation; the other wavelength, absorbed equally in oxygenated and deoxygenated hemoglobin, measures blood volume. The simultaneous electrode recordings give an electrophysiological measure of the underlying neuronal activity. The continuous recording makes it possible to distinguish between ongoing signals and stimulus-evoked responses. This technique will form the basis of the current project, giving a unique combination of tools to answer the questions at hand.