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Abstract:
Head direction (HD) neurons are thought to provide the mammalian brain with an internal sense of direction. These cells - which selectively increase their firing when the animal's head points in a specific direction - use the spike rate to encode HD with a high signal-to-noise ratio. In the present work, we analyzed spike train features of presubicular HD cells recorded juxtacellularly in passively-rotated rats. We found that HD neurons could be classified into two groups based on their propensity to fire spikes at short interspike intervals. 'Bursty' neurons displayed distinct spike waveforms and were weakly but significantly more modulated by HD compared to 'non-bursty' cells. In a subset of HD neurons, we observed the occurrence of spikelets - small amplitude 'spike-like' events - whose HD tuning was highly correlated to that of the co-recorded juxtacellular spikes. Bursty and non-bursty HD cells, as well as spikelets, were also observed in freely-moving animals during natural behavior. We speculate that spike bursts and spikelets might contribute to PreS HD coding by enhancing its accuracy and transmission reliability to downstream targets.
