Biology subjects

Moore, J. J.

Publications and source records attributed to Moore, J. J..

4 recordsLinked to original sources

bioRxiv2021

Behaviorally emergent hippocampal place maps remain stable during memory recall

The hippocampus is critical for the formation and recall of episodic memories1, 2 which store past experience of events ( what) occurring at particular locations ( where) in time ( when). Hippocampal place cells, pyramidal neurons which show location-specific modulation of firing rates during navigation3, 4, together form a spatial representation of the environment. It has long been hypothesized that place cells serve as the neural substrate for long-term episodic memory of space5, 6. However, recent studies call to question this tenet of the field by demonstrating unexpected levels of representational drift in hippocampal place cells with respect to the duration of episodic memories in mice7, 8. In the present study, we examined behaviorally driven long-term organization of the place map, to resolve the relationship between memory and place cells. Leveraging the stability of two-photon calcium imaging, we tracked activity of the same set of CA1 pyramidal neurons during learning and memory recall in an operant, head-fixed, odorcued spatial navigation task. We found that place cells are rapidly recruited into task-dependent spatial maps, resulting in emergence of orthogonal as well as overlapping representations of space. Further, task-selective place cells used a diverse set of remapping strategies to represent changing task demands that accompany learning. We found behavioral performance dependent divergence of spatial maps between trial types occurs during learning. Finally, imaging during remote recall spanning up to 30 days revealed increased stabilization of learnt place cell maps following memory consolidation. Our findings suggest that a subset of place cells is recruited by rule based spatial learning, actively reconfigured to represent task-relevant spatial relationships, and stabilized following successful learning and consolidation.

neuroscience↗

bioRxiv2021

Hippocampal representations of distance, space, and direction and their plasticity predict navigational performance

The hippocampus is implicated in episodic memory and allocentric spatial navigation. However, spatial selectivity is insufficient to navigate; one needs information about the distance and direction to the reward on a specific journey. The nature of these representations, whether they are expressed in an episodic-like sequence, and their relationship with navigational performance are unknown. We recorded single units from dorsal CA1 of the hippocampus while rats navigated to an unmarked reward zone defined solely by distal visual cues, similar to the classic water maze. The allocentric spatial selectivity was substantially weaker than in typical real world tasks, despite excellent navigational performance. Instead, the majority of cells encoded path distance from the start of trials. Cells also encoded the rats allocentric position and head angle. Often the same cells multiplexed and encoded path distance, head direction and allocentric position in a sequence, thus encoding a journey-specific episode. The strength of neural activity and tuning strongly correlated with performance, with a temporal relationship indicating neural responses influencing behavior and vice versa. Consistent with computational models of associative Hebbian learning, neural responses showed increasing clustering and became better predictors of behaviorally relevant variables, with neurometric curves exceeding and converging to psychometric curves. These findings demonstrate that hippocampal neurons multiplex and exhibit highly plastic, task- and experience-dependent tuning to path-centric and allocentric variables to form an episode, which could mediate navigation.

neuroscience↗

bioRxiv2020

The dendritic spatial code: branch-specific place tuning and its experience-dependent decoupling

Dendrites of pyramidal neurons integrate different sensory inputs, and non-linear dendritic computations drive feature selective tuning and plasticity. Yet little is known about how dendrites themselves represent the environment, the degree to which they are coupled to their soma, and how that coupling is sculpted with experience. In order to answer these questions, we developed a novel preparation in which we image soma and connected dendrites in a single plane across days using in vivo two-photon microscopy. Using this preparation, we monitored spatially tuned activity in area CA3 of the hippocampus in head-fixed mice running on a linear track. We identified "place dendrites", which can stably and precisely represent both familiar and novel spatial environments. Dendrites could display place tuning independent of their connected soma and even their sister dendritic branches, the first evidence for branch-specific tuning in the hippocampus. In a familiar environment, spatially tuned somata were more decoupled from their dendrites as compared to non-tuned somata. This relationship was absent in a novel environment, suggesting an experience dependent selective gating of dendritic spatial inputs. We then built a data-driven multicompartment computational model that could capture the experimentally observed correlations. Our model predicts that place cells exhibiting branch-specific tuning have more flexible place fields, while neurons with homogenous or co-tuned dendritic branches have higher place field stability. These findings demonstrate that spatial representation is organized in a branch-specific manner within dendrites of hippocampal pyramidal cells. Further, spatial inputs from dendrites to soma are selectively and dynamically gated in an experience-dependent manner, endowing both flexibility and stability to the cognitive map of space. One sentence summaryHippocampal pyramidal cells show branch-specific tuning for different place fields, and their coupling to their soma changes with experience of an environment.

neuroscience↗

bioRxiv2016

Dynamics of Cortical Dendritic Membrane Potential and Spikes in Freely Behaving Rats

Neural activity in vivo is primarily measured using extracellular somatic spikes, which provide limited information about neural computation. Hence, it is necessary to record from neuronal dendrites, which generate dendritic action potentials (DAP) and profoundly influence neural computation and plasticity. We measured neocortical sub- and supra-threshold dendritic membrane potential (DMP) from putative distal-most dendrites using tetrodes in freely behaving rats over multiple days with a high degree of stability and sub-millisecond temporal resolution. DAP firing rates were several fold larger than somatic rates. DAP rates were modulated by subthreshold DMP fluctuations which were far larger than DAP amplitude, indicting hybrid, analog-digital coding in the dendrites. Parietal DAP and DMP exhibited egocentric spatial maps comparable to pyramidal neurons. These results have important implications for neural coding and plasticity.\n\nOne Sentence SummaryMeasurement of cortical dendritic membrane potential for several days in freely behaving rats reveals disproportionate dendritic spiking and analog and digital coding.

neuroscience↗