Biology subjects

Person, A. L.

Publications and source records attributed to Person, A. L..

3 recordsLinked to original sources

bioRxiv2018

Pathway specific drive of cerebellar Golgi cells reveals integrative rules of cortical inhibition

Cerebellar granule cells (GrCs) constitute over half of all neurons in the vertebrate brain and are proposed to decorrelate convergent mossy fiber inputs in service of learning. Interneurons within the granule cell layer, Golgi cells (GoCs), are the primary inhibitors of this vast population and therefore play a major role in influencing the computations performed within the layer. Despite this central function for GoCs, few studies have directly examined how GoCs integrate inputs from specific afferents which vary in density to regulate GrC population activity. We used a variety of methods in mice of either sex to study feedforward inhibition recruited by identified MFs, focusing on features that would influence integration by GrCs. Comprehensive 3D reconstruction and quantification of GoC axonal boutons revealed tightly clustered boutons that focus feedforward inhibition in the neighborhood of GoC somata. Acute whole cell patch clamp recordings from GrCs in brain slices showed that despite high bouton density, fast phasic inhibition was very sparse relative to slow spillover mediated inhibition. Furthermore, dynamic clamp simulating inhibition combined with optogenetic mossy fiber activation supported the predominant role of slow spillover mediated inhibition. Whole cell recordings from GoCs revealed a role for the density of active MFs in preferentially driving them. Thus, our data provide empirical conformation of predicted rules by which MFs activate GoCs to regulate GrC activity levels.

neuroscience↗

bioRxiv2018

Graded and bidirectional control of real-time reach kinematics by the cerebellum

The rules governing the relationship between cerebellar output and movement production remain unknown despite the well-recognized importance of the cerebellum in motor learning and precision. In this study, we investigated how cerebellar output sculpts reach behavior in mice by manipulating neural activity in the anterior interposed nucleus (IntA) in closed-loop with ongoing behavior. Optogenetic modulation of cerebellar output revealed monotonically graded and bidirectional control of real-time reach velocity by IntA. Furthermore, kinematic effects were relatively context invariant, suggesting that cerebellar output summates with ongoing motor commands generated elsewhere throughout the reaching movement. These results characterize the relationship between cerebellar output modulation and reach behavior as a bidirectional and scalable kinematic command signal. Our findings illustrate how learned, predictive coding in the cerebellar cortex could be actuated through the cerebellar nuclei to contribute in real time to purposive motor control.

neuroscience↗

bioRxiv2017

Morphological constraints on cerebellar granule cell combinatorial diversity

Combinatorial expansion by the cerebellar granule cell layer (GCL) is fundamental to theories of cerebellar contributions to motor control and learning. Granule cells sample approximately four mossy fiber inputs and are thought to form a combinatorial code useful for pattern separation and learning. We constructed a spatially realistic model of the cerebellar granule cell layer and examined how GCL architecture contributes to granule cell (GrC) combinatorial diversity. We found that GrC combinatorial diversity saturates quickly as mossy fiber input diversity increases, and that this saturation is in part a consequence of short dendrites, which limit access to diverse inputs and favor dense sampling of local inputs. This local sampling also produced GrCs that were combinatorially redundant, even when input diversity was extremely high. In addition, we found that mossy fibers clustering, which is a common anatomical pattern, also led to increased redundancy of GrC input combinations. We related this redundancy to hypothesized roles of temporal expansion of GrC information encoding in service of learned timing, and show that GCL architecture produces GrC populations that support both temporal and combinatorial expansion. Finally, we used novel anatomical measurements from mice of either sex to inform modeling of sparse and filopodia-bearing mossy fibers, finding that these circuit features uniquely contribute to enhancing GrC diversification and redundancy. Our results complement information theoretic studies of granule layer structure and provide insight into the contributions of granule layer anatomical features to afferent mixing.\n\nSignificance StatementCerebellar granule cells are among the simplest neurons, with tiny somata and on average just four dendrites. These characteristics, along with their dense organization, inspired influential theoretical work on the granule cell layer (GCL) as a combinatorial expander, where each granule cell represents a unique combination of inputs. Despite the centrality of these theories to cerebellar physiology, the degree of expansion supported by anatomically realistic patterns of inputs is unknown. Using modeling and anatomy, we show that realistic input patterns constrain combinatorial diversity by producing redundant combinations, which nevertheless could support temporal diversification of like-combinations, suitable for learned timing. Our study suggests a neural substrate for producing high levels of both combinatorial and temporal diversity in the GCL.

neuroscience↗