Senzai Y, Scanziani M. (2022) Science 377 (6609): 999–1004.  (link, PDF)

Since the discovery of REM sleep, the nature of the rapid eye movements that characterize this sleep phase has remained elusive. Do they reveal gaze shifts in the virtual environment of dreams or simply reflect random brainstem activity? We harnessed the head direction (HD) system of the mouse thalamus, a neuronal population whose activity reports, in awake mice, their actual HD as they explore their environment and, in sleeping mice, their virtual HD. We discovered that the direction and amplitude of rapid eye movements during REM sleep reveal the direction and amplitude of the ongoing changes in virtual HD. Thus, rapid eye movements disclose gaze shifts in the virtual world of REM sleep, thereby providing a window in the cognitive processes of the sleeping brain. Our results further suggest the existence of a global coordination among distinct brain systems during REM sleep, which may underlie vivid perception in dreams.

Previewed by: De Zeeuw CI and Canto CB. Interpreting thoughts during sleep.

Featured by: Science Magazine Podcast (from 9min50sec), NewScientist, The Conversation, etc

Senzai Y*, Fernandez-Ruiz A*, Buzsáki G. (2019) Neuron 101, 500-513.  (link, PDF)

The relationship between mesoscopic local field potentials (LFPs) and single-neuron firing in the multi-layered neocortex is poorly understood. Simultaneous recordings from all layers in the primary visual cortex (V1) of the behaving mouse revealed functionally defined layers in V1. The depth of maximum spike power and sink-source distributions of LFPs provided consistent laminar landmarks across animals. Coherence of gamma oscillations (30-100 Hz) and spike-LFP coupling identified six physiological layers and further sublayers. Firing rates, burstiness, and other electrophysiological features of neurons displayed unique layer and brain state dependence. Spike transmission strength from layer 2/3 cells to layer 5 pyramidal cells and interneurons was stronger during waking compared with non-REM sleep but stronger during non-REM sleep among deep-layer excitatory neurons. This indicates different routing of information in the neocortex during waking and sleep. These results bridge mesoscopic LFPs and single-neuron interactions with laminar structure in V1.

Previewed by: Vinck M and Perrenoud Q. Layers of rhythms – from cortical anatomy to dynamics.

Senzai Y, Buzsáki G. (2017) Neuron 93 (3), 691-704.  (link, PDF)

The hippocampal dentate gyrus is often viewed as a segregator of upstream information. Physiological support for such a function has been hampered by a lack of well-defined characteristics that can identify granule cells and mossy cells. We developed an electrophysiology-based classification of dentate granule cells and mossy cells in mice that we validated by optogenetic tagging of mossy cells. Granule cells exhibited sparse firing and showed only modest changes when the mouse was tested in different mazes in the same room. In contrast, mossy cells were more active and showed stronger remapping of place fields under the same conditions. Although the granule cell-mossy cell synapse was strong and facilitating, mossy cells rarely “inherited” place fields from single granule cells. Our findings suggest that the granule cells and mossy cells could be modulated separately, and their joint action may be critical for pattern separation.

Previewed by: Nakazawa K. Dentate mossy cell and pattern separation.