Ins and outs of dendritic integration in awake mice

Neurons are frequently viewed as discrete input-output computers; decoding synaptic inputs to their dendrites to generate correct outputs from their soma, through ‘dendritic integration’. Yet fundamental properties, such as spatio-temporal patterns of synaptic inputs, and the number of inputs required to generate an output in awake animals, remain unknown. We combined simultaneous voltage and calcium imaging from spiny dendrites, with somatic electrical recording from cerebellar Purkinje neurons to investigate dendritic integration in awake mice. Here we show spatio-temporal patterns of dendritic signaling and their non-linear relationship with somatic output and provide an estimate for the number of synaptic inputs required to generate a somatic output. Sub-millisecond two-photon imaging detected rapid and localized sub- and supra-threshold dendritic signaling and revealed how high frequency electrical dendritic inputs concurrently regulate somatic output and permit isolated dendritic computations with millisecond precision. These findings explore the complexity of dendritic signaling and support the hypothesis that dendritic processes behave as fundamental computational units.