Biological cortical neurons are remarkably sophisticated computational devices,temporally integrating their vast synaptic input over an intricate dendritic tree,subject to complex, nonlinearly interacting internal biological processes. A recentstudy proposed to characterize this complexity by fitting accurate surrogate modelsto replicate the input-output relationship of a detailed biophysical cortical pyramidalneuron model and discovered it needed temporal convolutional networks (TCN)with millions of parameters. Requiring these many parameters, however, couldbe the result of a misalignment between the inductive biases of the TCN andcortical neuron’s computations. In light of this, and with the aim to explorethe computational implications of leaky memory units and nonlinear dendriticprocessing, we introduce the Expressive Leaky Memory (ELM) neuron model, abiologically inspired phenomenological model of a cortical neuron. Remarkably, byexploiting a few such slowly decaying memory-like hidden states and two-layerednonlinear integration of synaptic input, our ELM neuron can accurately matchthe aforementioned input-output relationship with under ten-thousand trainableparameters. To further assess the computational ramifications of our neuron design,we evaluate on various tasks with demanding temporal structures, including theLong Range Arena (LRA) datasets, as well as a novel neuromorphic dataset basedon the Spiking Heidelberg Digits dataset (SHD-Adding). Leveraging a largernumber of memory units with sufficiently long timescales, and correspondinglysophisticated synaptic integration, the ELM neuron proves to be competitive onboth datasets, reliably outperforming the classic Transformer or Chrono-LSTMarchitectures on latter, even solving the Pathfinder-X task with over 70\% accuracy(16k context length). These findings indicate the importance of inductive biasesfor efficient surrogate neuron models and the potential for biologically motivatedmodels to enhance performance in challenging machine learning tasks.
The Expressive Leaky Memory Neuron: an Efficient and Expressive Phenomenological Neuron Model Can Solve Long-Horizon Tasks.
Aaron Spieler Nasim Rahaman Georg Martius Bernhard Schölkopf Anna Levina