Complex spike firing adapts to saliency of inputsand engages readiness to act

Abstract

The cerebellum is involved in cognition next to motor coordination. During complex tasks, climbing fiber input to the cerebellum can deliver seemingly opposite signals, covering both motor and non-motor functions. To elucidate this ambiguity, we hypothesized that climbing fiber activity represents the saliency of inputs leading to action-readiness. We addressed this hypothesis by recording Purkinje cell activity in lateral cerebellum of awake mice learning go/no-go decisions based on entrained saliency of different sensory stimuli. As training progressed, the timing of climbing fiber signals switched in a coordinated fashion with that of Purkinje cell simple spikes towards the moment of occurrence of the salient stimulus that required action. Trial-by-trial analysis indicated that emerging climbing fiber activity is not linked to individual motor responses or rewards per se, but rather reflects the saliency of a particular sensory stimulus that engages a general readiness to act, bridging the non-motor with the motor functions. In brief O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=199 SRC="FIGDIR/small/314534v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@c319edorg.highwire.dtl.DTLVardef@db527eorg.highwire.dtl.DTLVardef@104e94eorg.highwire.dtl.DTLVardef@17115f2_HPS_FORMAT_FIGEXP M_FIG C_FIG Mice were trained to identify the saliency of different sensory inputs in that they had to learn to ignore a prominent sound cue and respond to a light tactile cue in a Go/No-Go licking task. As the mice learned to discriminate the two inputs and respond to the proper signal, the Purkinje cells in the lateral cerebellum switched their climbing fiber activity (i.e., complex spike activity) towards the moment of occurrence of the salient stimulus that required a response, while concomitantly shifting the phase of their simple spike modulation. Trial-by-trial analysis indicates that the emerging climbing fiber activity is not linked to the occurrence of the motor response or reward per se, but rather reflects the saliency of a particular sensory stimulus engaging a general readiness to act.