Speaker
Description
With recent advances in technology it has become possible to record 100s of neurons simultaneously from awake behaving animals. The analysis of such high-dimensional neuronal activity has revealed two interesting features: 1. neuronal activity is confined to a rather low-dimensional sub-manifold and animals find it very difficult (if not impossible) to change these low-dimensional intrinsic manifolds (2) Within the manifold, neuronal activity is organized as temporal (and some times spatial) sequences. The two properties provide new insights into the representation of information in the brain. In my talk, I will discuss the origin of these two features of the neuronal activity.
First, I will argue that the low-dimensional manifold of cortical activity are consequence of the function the networks have learned to perform. I will show that within manifold changes entail small changes in the synaptic weights, while outside manifold changes require a massive rewiring of the whole network. This observation provides an explanation of why it is difficult to change the intrinsic manifold of neuronal activity.
Next, to address how within a manifold neuronal activity is organized as a temporal sequences, I will focus on networks with distance dependent connectivity. For such networks we have found that when (1) neurons project a small fraction of their outputs to a preferential direction and (2) the preferred directions of neighboring neurons are similar, the network can generate temporal sequences without supervised or unsupervised learning. This generative rule implies that the need for a ‘correlated spatial anisotropic connectivity’. Such connectivity can arise when neighbouring neurons have similar shapes. In addition, I will argue that spatially patchy patterns of neuromodulator release not only allow for the formation of temporal sequences but also provide a biological plausible way to dynamical change the arrangement of sequences. Finally, I will discuss the implications of these results for brain dysfunction and control of neuronal activity dynamics.
