P026 Prospective and retrospective coding in cortical neurons
Simon Brandt1, Paul Haider*,1, Mihai A. Petrovici1, Walter Senn1, Katharina A. Wilmesa,1, Federico Beniteza,1
1Department of Physiology, University of Bern, Switzerland ashared senior authorship
*Email: paul.haider@unibe.ch
Introduction Brains can process sensory information from different modalities at astonishing speed; this is surprising as already the integration of inputs through the membrane causes a delayed response Fig. 1d. Experiments reveal a possible explanation for the fast processing, showing that neurons can advance their output firing rate with respect to their input current, a concept which we refer to as prospective coding [1]. The combination of retrospective (a delayed response) and prospective coding enables neurons to perform temporal processing. While retrospective coding emerges from the inherent delays of neurons, the underlying mechanisms of prospective coding, however, are not completely understood.
Methods In this work, we elucidate cellular mechanisms which can explain prospective firing in cortical neurons. We use simulation-based inference to investigate the parameters of the Hodgkin-Huxley model [2] with respect to its ability to fire prospective and retrospective. Based on this analysis, we derive a reduced model that allows us manipulate the temporal response of the Hodgkin-Huxley neurons. Further on, we derive rate based models of neurons which include adaption processes on arbitrary time scales to investigate advances on longer time scales.
Results We show that the spike generation mechanism can be the source for the prospective (advanced) or retrospective (delayed) response as shown for prospective firing (Fig. 1a) in cortical-like neurons [3,4] (Fig. 1b, green) and retrospective firing (Fig. 1c) in hippocampal-like neurons [5,6] (Fig. 1b, orange). Further, we analyse the Hodgkin-Huxley dynamics to derive a reduced model to manipulate the timing of the neuron’s output by tuning three parameters (Fig. 1d-h). We further show that slow adaptation processes, such as spike-frequency adaptation or deactivating dendritic currents, can generate prospective firing for inputs that undergo slow temporal modulations. In general, we show that adaptation processes at different time scales can cause advanced neuronal responses to time-varying inputs that are modulated on the corresponding time scales.
Discussion The results of this work contribute to the understanding of how fast processing (prospective coding) and short-term memory (retrospective coding) can be achieved in the brain on the level of single neurons and might guide further experiments. Prospectivity and retrospectivity may be important for several cognitive functions. The interplay of the two provides a powerful framework for temporal processing by shifting signals in time. The insights are highly beneficial for biologically plausible learning algorithms used for temporal processing and their implementation on neuromorphic hardware [7-9]. Figure 1. (a) Hodgkin-Huxley neurons can be prospective for cortical neurons (b, green) and retrospective (c) for parameters fitted to hippocampal neurons (b, orange). (d) Because a neuron integrates input through its membrane, a response of the neuron is expected to be delayed by the membrane. If the output of a neuron can be advanced with respect to its input, a prospective mechanism needs to exist. With Acknowledgements We would like to express particular gratitude for the ongoing support from the Manfred Stärk Foundation. Our work has greatly benefited from access to the Fenix Infrastructure resources, which are partially funded through the ICEI project under the grant agreement No. 800858. This includes access to Piz Daint at the Swiss National Supercomputing Centre, Switzerland. References
