Effects of spatial attention on neural processing in rhesus’ V1: a simultaneous electrophysiology and fMRI study

Attention is a cognitive function thought to enhance our ability to select, process, and perceive only a behaviorally relevant fraction of the immense sensory input impinging on our receptors (Knudsen, 2007). Early electrophysiological studies in primates demonstrate that attention can modulate substantially the firing rate of single cells in extrastriate visual areas but has no or little impact in the primary visual cortex (Moran & Desimone, 1985). In contrast, attention has been linked to strong bloodoxygenlevel-dependent (BOLD) signal modulations in human subjects (Gandhi et al., 1999). Our goal is to understand how selective visual spatial attention modulates the neuronal activity in primary visual cortex (V1) and how these effects are reflected in the different signals (single unit activity, local field potentials, and BOLD). To this end, we have trained two rhesus macaques to perform an orientation-change detection task in high field fMRI scanners (4.7T, 7T) while we can simultaneously acquire highresolution fMRI maps and electrophysiological signals. Preliminary results suggest that attention modulates the BOLD and electrophysiological signals in distinct ways. We are currently trying to address the layer specificity of the effects by using MRI compatible multicontact probes and implanted RF coils that provide ultra-high resolution maps of the fMRI activations