Reading out a spatiotemporal population code by imaging neighbouring parallel fibre axons in vivo

Abstract

The spatiotemporal pattern of synaptic inputs to the dendritic tree is crucial for synaptic integration and plasticity. However, it is not known if input patterns driven by sensory stimuli are structured or random. Here we investigate the spatial patterning of synaptic inputs by directly monitoring presynaptic activity in the intact mouse brain on the micron scale. Using in vivo calcium imaging of multiple neighbouring cerebellar parallel fibre axons, we find evidence for clustered patterns of axonal activity during sensory processing. The clustered parallel fibre input we observe is ideally suited for driving dendritic spikes, postsynaptic calcium signalling, and synaptic plasticity in downstream Purkinje cells, and is thus likely to be a major feature of cerebellar function during sensory processing.

Improving data quality in neuronal population recordings

“…Motion in Z is more difficult to correct, since the neighboring planes are typically not recorded. Generally, point spread functions (PSFs) are extended in Z, making motion artifacts due to small Z movements less problematic 125, 126 . In cases with large Z movement, multiplane imaging 127 and online motion correction 120, 128 can help minimize artifacts.…”

Clustered structural and functional plasticity of dendritic spines

“…This is compatible with the finding that synaptic dynamism occurs without major reorganization of dendritic or axonal arbors (Mizrahi and Katz, 2003; Trachtenberg et al, 2002). In addition, adjacent spines may receive locally convergent inputs from axons that originate from the same neuronal assembly and exhibit similar activity patterns (Kleindienst et al, 2011; Takahashi et al, 2012; Wilms and Hausser, 2015). In such a scenario, clustered plasticity at postsynaptic sites can emerge from shared input patterns due to activity-dependent plasticity rules.…”

Nonspecific synaptic plasticity improves the recognition of sparse patterns degraded by local noise

“…It is therefore conceivable that local noise in stimulus space is propagated within clusters of parallel fibers, hence that the natural neighborhood relationships are preserved. At first sight, the clusters of co-activated PFs observed by Wilms and Häusser39 may be too large (median distance of 11 μm) for the very local action of nsLTD in the present simulations (Fig. 5), but the labeling of PFs was too sparse in this imaging study to reliably measure cluster size.…”

“…There are no indications that neighboring PF synapses on a PC originate from neighboring granule cells in the granular layer3955, the projections seem to be rather divergent. But in their recent technically ingenious study, Wilms and Häusser39 did find that behaviorally relevant stimuli excite clusters of neighboring parallel fibers, in spite of their being coded in a distributed fashion in the granular layer. It is therefore conceivable that local noise in stimulus space is propagated within clusters of parallel fibers, hence that the natural neighborhood relationships are preserved.…”