Sharp-wave ripple features in macaques depend on behavioral state and cell-type specific firing.

Sharp-wave ripples (SWRs) are spontaneous, synchronized neural population events in the hippocampus widely thought to play a role in memory consolidation and retrieval. They occur predominantly in sleep and quiet immobility, and in primates, they also appear during active visual exploration. Typical measures of SWRs in behaving rats include changes in the rate of occurrence, or in the incidence of specific neural ensemble activity contained within the categorical SWR event.

Sharp-Wave Ripples in Primates Are Enhanced near Remembered Visual Objects.

The hippocampus plays an important role in memory for events that are distinct in space and time. One of the strongest, most synchronous neural signals produced by the hippocampus is the sharp-wave ripple (SWR), observed in a variety of mammalian species during offline behaviors, such as slow-wave sleep [1-3] and quiescent waking and pauses in exploration [4-8], leading to long-standing and widespread theories of its contribution to plasticity and memory during these inactive or immobile states [9-14]. Indeed, during sleep and waking inactivity, hippocampal SWRs in rodents appear to support spatial long-term and working memory [4, 15-23], but so far, they have not been linked to memory in primates.

Hippocampal gamma-band Synchrony and pupillary responses index memory during visual search.

Memory for scenes is supported by the hippocampus, among other interconnected structures, but the neural mechanisms related to this process are not well understood. To assess the role of the hippocampus in memory-guided scene search, we recorded local field potentials and multiunit activity from the hippocampus of macaques as they performed goal-directed search tasks using natural scenes. We additionally measured pupil size during scene presentation, which in humans is modulated by recognition memory.

Pupillary responses and memory-guided visual search reveal age-related and Alzheimer's-related memory decline.

Episodic memory - composed of memory for unique spatiotemporal experiences - is known to decline with aging, and even more severely in Alzheimer 's disease (AD). Memory for trial-unique objects in spatial scenes depends on the integrity of the hippocampus and interconnected structures that are among the first areas affected in AD. We reasoned that memory for objects-in-scenes would be impaired with aging, and that further impairments would be observed in AD.

Sharp Wave Ripples during Visual Exploration in the Primate Hippocampus.

Unlabelled: Hippocampal sharp-wave ripples (SWRs) are highly synchronous oscillatory field potentials that are thought to facilitate memory consolidation. SWRs typically occur during quiescent states, when neural activity reflecting recent experience is replayed. In rodents, SWRs also occur during brief locomotor pauses in maze exploration, where they appear to support learning during experience.

Saccades during visual exploration align hippocampal 3-8 Hz rhythms in human and non-human primates.

Visual exploration in primates depends on saccadic eye movements (SEMs) that cause alternations of neural suppression and enhancement. This modulation extends beyond retinotopic areas, and is thought to facilitate perception; yet saccades may also influence brain regions critical for forming memories of these exploratory episodes. The hippocampus, for example, shows oscillatory activity that is generally associated with encoding of information.

How macaques view familiarity and gaze in conspecific faces.

The pattern of visual fixations on an image depends not only on the image content but also on the viewer's disposition and on the function (or pathology) of underlying neural circuitry. For example, human viewers display changes in viewing patterns toward face images that differ in gaze direction or in the viewer's familiarity with the face. Macaques share many face processing abilities with humans, and their neural circuitry is used to understand perception across species, yet their viewing responses to gaze and familiarity of faces is poorly understood.