Cell Assemblies: Possible Building Blocks of Cognition Gamma-band Responses Reflect Wordipseudoword

According to one brain-theoretical view, high~!:.brainful1ctionsarebased on processing_!!l1j.ts called cell as~~mbJiys. <::ell assemblies are large groups of corticalpyramidal neurons with strong and reclproc-al internal connections. C~lla,ssemblies develop in a randomIy-connected neuronal network when sets of neurons are frequently attive-simillfaneolisly so that their connectionsEstrengthen (Hebb's law, 1992). Neurons making up one assembly do not need to be located in a small cortical area. They may be distributed widely over various cortical regions. Such transcortical assemblies are likely to be held together through long axonsof pyramidal cells which are well-known to connect distant cortical areas Due to strong intra-assembly connections, excitation of some neurons of an assembly leads to spreading activation in the network and, finally, to an "ign'ilioiiiJ>&tthe whole_ assembly. Overshooting activity will occur in the cortex when too many ,assemblies ig1\:rt~at the same time. Therefore, a regulation mechanism is required which keeps the level of cortical excitation close to a target value (Braitenberg, 1978). This regulatiop.ll1ech-anism guarantees that only one or a limited number of assemblies will igrilit~ at a time. What is the purpose of transcortical assemblies? One obvious answer is the fol-lowing:tianscortical assembhesi11ake it possible to "bind" information represented in different parts of the corte~. Such binding may occur between neurons in the visual ~iSteJ!l:stihiulated by features of a perceived object. If assemblies include vari