Neuronal Activity in Cortical and Thalamic Networks : A study with multiple microelectrodes

One of the major problems with which neurophysiological research has been confronted, in recent years, is the way in which the brain deals with the information that it receives over the sensory pathways. The study of this problem has been much enhanced by the development of techniques for the recording of the activity of single neurons. The use of such techniques has provided valuable information in two fields of investigation. One field, the electrophysiology of the brain cell: in this respect it has been found that electrical characteristics of cortical and thalamic neurons are very similar to those of neurons located elsewhere in the central nervous system (4, 5, 11, 16, 22), Another field, the study of the patterns of response of single brain cells to peripheral stimulation: in this respect it has been found that the latency of response, the number of spikes and the intervals between spikes generated by each individual neuron are related to the intensity, the frequency and the position of the peripheral stimulus (2, 3, 6, 7-10, 15, 17, 18, 23). Thus, cerebral neurons participate in the coding and the displaying of information upon the maps which, in the sensory receiving areas of the brain, represent the spatial, temporal, and other characteristics of events that occur in the outside world. Little is known, however, about the way in which the coded information displayed upon these maps is selected and organized in order to result in the processes which we call perception and integration. Whatever the mechanism of these processes may be, it is evident that, since it involves comparison, selection, and organization of sensory and memory data, it cannot be based on the activity of isolated neurons but it must be based on the interrelated activities of the large number of neurons which, with their connections, form the complex networks present in the brain stem and in the cortex. It is well known that some neurons in these networks are spontaneously