Dendritic Spikes in Sensory Perception

Abstract

What is the function of dendritic spikes? One might argue that they provide conditions for neuronal plasticity or that they are essential for neural computation. However, despite a long history of dendritic research, the physiological relevance of dendritic spikes in brain function remains unknown. This could stem from the fact that most studies on dendrites have been performed in vitro. Fortunately, the emergence of novel techniques such as improved two-photon microscopy, genetically encoded calcium indicators (GECIs), and optogenetic tools has provided the means for vital breakthroughs in in vivo dendritic research. These technologies enable the investigation of the functions of dendritic spikes in behaving animals, and thus, help uncover the causal relationship between dendritic spikes, and sensory information processing and synaptic plasticity. Understanding the roles of dendritic spikes in brain function would provide mechanistic insight into the relationship between the brain and the mind. In this review article, we summarize the results of studies on dendritic spikes from a historical perspective and discuss the recent advances in our understanding of the role of dendritic spikes in sensory perception.

Keywords: bottom-up processing; dendritic integration; dendritic spike; neocortex; pyramidal neuron; sensory perception; top-down control.

Figure 1

Hypothetical model for mechanisms of sensory perception. (A) Animal perception, assumed by behavioral responses (i.e., hit or miss behaviors), correlates with the late component in a stimulus intensity discrimination task. Even though the intensity of sensory stimulation was identical, animal behavior responses were different and perceptual behaviors correlated with the late neural activities. (B) A novel mechanism for the late activity. Top-down inputs (here from M2) propagate from the bottom to the top layers of the sensory cortex in a short time window to reliably drive dendritic spiking and BAC firing (~50 ms in A). We termed this top-down input pattern, “top-down coincident input or TCI”. We hypothesized that the number of neurons that had a Ca²⁺ spike during perception (Hits) behavior is larger than that during no perception (Misses). BAC, backpropagating action-potential-activated calcium spike; BPAP, backpropagating action potential. Panel (A) is reprinted with permission from Cauller (1995).