The dichotomy between two groups of workers on neuroelectrical activity is retarding progress. To study the interrelations between neuronal unit spike activity and compound field potentials of cell populations is both unfashionable and technically challenging. Neither of the mutual disparagements is justified: that spikes are to higher functions as the alphabet is to Shakespeare and that slow field potentials are irrelevant epiphenomena. Spikes are not the basis of the neural code but of multiple codes that coexist with nonspike codes. Field potentials are mainly information-rich signs of underlying processes, but sometimes they are also signals for neighboring cells, that is, they exert inf luence. This paper concerns opportunities for new research with many channels of wide-band (spike and slow wave) recording. A wealth of structure in time and three-dimensional space is different at each scale-micro-, meso-, and macroactivity. The depth of our ignorance is emphasized to underline the opportunities for uncovering new principles. We cannot currently estimate the relative importance of spikes and synaptic communication vs. extrasynaptic graded signals. In spite of a preponderance of literature on the former, we must consider the latter as probably important. We are in a primitive stage of looking at the time series of wide-band voltages in the compound, local field, potentials and of choosing descriptors that discriminate appropriately among brain loci, states (functions), stages (ontogeny, senescence), and taxa (evolution). This is not surprising, since the brains in higher species are surely the most complex systems known. They must be the greatest reservoir of new discoveries in nature. The complexity should not deter us, but a dose of humility can stimulate the f low of imaginative juices.A profound revolution lurks in our basic concept of how the information-bearing elements of the nervous system communicate. Two views coexist, mutually derogatory but not mutually exclusive, with little effort to discover the wider whole.* The dichotomy concerns such central questions about how brains work that I feel driven to put it under a spotlight.One common view, which we may dub the unit window, is that, with rare exceptions, neural communication consists of successions of nerve impulses in neurons, encoding messages in their intervals, decoding at axonal terminals into an analog dose of transmitter that restarts the cycle in the next cell. A principal problem in explaining higher functions is seen as the adequacy of sampling of units.The contrasting view, which we may call the population window, does not deny any of this except the implication that it embraces all the significant aspects of neural activity in organized cell assemblies. Major features of the dynamics of non-randomly assembled arrays, on this view, include their nonspike, more slowly fluctuating potentials, their changing degrees of population synchrony, and their rhythms and largescale patterns. These and other features are worth attention wh...

No abstract

No abstract

To compare the ongoing electrical activity in possibly homologous structures of reptiles and mammals, the electrographic activity (micro-EEG) from major parts of the cortex of unanesthetized turtles (Pseudemys) and geckos (Gekko) was recorded with and without acute and chronic stimuli, physostigmine and atropine. Electrodes were placed in the medial cortex (MC) and in the dorsal cortex (DC), the possible homologs of the mammalian hippocampus and transitional or/and isocortex, respectively. The resting corticograms (1–50 Hz) are different in the two cortical areas. Both are wide-band; power falls steadily with frequency above a single maximum about 2 Hz. The MC has a nonrhythmic, low-voltage activity with occasional superimposed large sharp waves (LSWs), generally biphasic, 100–300 µV and lasting 0.25–0.75 s. The DC has smaller amplitudes (ca. 3–6 dB) at all frequencies and fewer LSWs. Reptilian LSWs are reminiscent of mammalian hippocampal sharp waves or spikes, a correlate of decreased arousal. The immobility-related rhythmic slow activity (theta), so characteristic of the hippocampus in a number of mammals, was not found in the cortex of either species of reptile under a variety of conditions. We cannot exclude the possibility of movement-related theta waves. Physostigmine injection does not produce theta, although it acts like an arousing stimulus, producing a disappearance of the LSWs and a substantial increase in the amplitude of the frequencies 12–24 Hz; these changes were more obvious in the DC. Atropine reversed the effects of physostigmine. Theta may represent a trait of the more highly differentiated hippocampal field of mammals. The condition represented by these reptiles, in which the EEG differs between parts of the pallium but without theta or reciprocal changes in the MC and DC, may be an earlier evolutionary stage. A distinctive reptilian EEG is not recognizable in Pseudemys and Gekko_tbut a number of differences from the EEG in familiar mammals are shared by these two neurologically quite different reptiles.