Hebb's Dream: The Resurgence of Cell Assemblies

What we are witnessing in modern neurophysiology is increasing empirical support for Hebb's views on the neural basis of behavior. While there is much more to be learned about the nature of distributed processing in the nervous system, it is safe to say that the observations made in the last 5 years are likely to change the focus of systems neuroscience from the single neuron to neural ensembles. Fundamental to this shift will be the development of powerful analytical tools that allow the characterization of the encoding algorithms employed by distinct neural populations. Currently, this is an area of research that is rapidly evolving.Further demonstration of a causal link between neural ensemble activity patterns and specific sensations or behaviors is necessary to demonstrate the relevance of population coding in the CNS. This issue is being approached in several ways. On one hand, information obtained at the molecular and cellular level is beginning to be applied to the investigation of circuit properties. For instance, ensemble recordings can now be combined with other neurobiological approaches, such as knockout genetics and/or the selective elimination of specific cell types (e.g.,McHugh et al. 1996xMcHugh, T.J, Blum, K.I, Tsien, J.Z, Tonegawa, S, and Wilson, M.A. Cell. 1996; 87: 1339–1349Abstract | Full Text | Full Text PDF | PubMed | Scopus (373)See all ReferencesMcHugh et al. 1996). These techniques will allow us to investigate what role a specific cellular population may play in information coding by large cell assemblies. At the other end of the spectrum, chronic and simultaneous multisite neural ensemble recordings can now be performed in behaving primates (Nicolelis et al., 1996, Soc. Neurosci. abstract). Since these recordings remain stable for many months, this opens the possibility of investigating how the learning of sensorimotor or cognitive tasks impacts the large-scale neuronal interactions within and between cortical and subcortical neural ensembles. These and other exciting developments promise to open a new era of investigation in systems neuroscience.