Oscillatory spiking activity in primate superior colliculus is related to spatial working memory

Abstract

Event Abstract Back to Event Oscillatory spiking activity in primate superior colliculus is related to spatial working memory Lee Lovejoy1* and Richard J. Krauzlis1 1 Salk Institute for Biological Studies, United States We report the presence of oscillatory spiking activity associated with memory-guided saccades in the primate superior colliculus (SC). Behavior contingent on spatial memory is associated with persistent activity in regions of the brain related to the planning and execution of movement. How this activity persists in the absence of a sensory stimulus is currently a matter of debate, and its resolution would be of great significance to understanding both working memory and memory-contingent control of behavior. One potential explanation is that spatial memory is stored as reverberant oscillatory activity (Goldman-Rakic, 1995). The oscillatory activity is triggered upon the disappearance of spatially specific sensory input; in turn, it drives persistent activity elsewhere in the circuit in the absence of visual input and thus serves as local working memory. Indeed, oscillatory activity associated with working memory has been observed in frontal and parietal cortical areas in both human and non-human primates performing working memory tasks. For example, persistent spiking activity can be observed prior to memory-guided movements in both brainstem and cortical areas, including the superior colliculus (SC), frontal eye fields (FEF), and lateral intraparietal area (LIP); corresponding oscillatory spiking activity in the gamma-band (30-80 Hz) has been observed in both FEF (Buneo et al, 2003) and LIP (Pesaran et al, 2002) during the same period. We examined persistent activity recorded in the intermediate and deep layers of the SC while monkeys performed memory-guided saccades. Using multi-taper spectral analysis, we detected the presence of a narrow peak in the power spectrum of spiking activity in a subset of SC neurons. For most such cells, the peak appeared in the gamma-band (30-80 Hz), while the remainder appeared in the beta band (15-30 Hz) with no clear distinction between them. The peak only appeared when the memory-guided saccades were directed into the response field of the neuron and only after the visual cue was extinguished. Therefore the oscillatory activity was temporally and spatially specific to the remembered saccade goal, and could thus serve as local storage of working memory. These results show that some superior colliculus neurons could have dynamic memory fields like those seen in cortex. These dynamic memory fields appear to be in register with the well-known retinotopic motor map for saccades found in the SC and could form a "memory map" which is a component of a distributed circuit for spatial working memory.