Patterns of hippocampal theta rhythm in the freely moving rat

Hippocampal theta oscillations are travelling waves

“…2). In agreement with several previous studies 27,30,34 , we found that theta oscillations start reversing their phase slightly below the pyramidal cell layer, as determined by the peak amplitude of sharp-wave-associated ripples and the reversal of sharp-wave polarity ( Fig. 1e and Supplementary Fig.…”

“…In other words, how does the phase of theta oscillations depend on the anatomical location of the recorded LFP? It is well known that the amplitude and phase of theta oscillations depend on the depth, or more precisely the lamina, of the observed signal [25][26][27] , because several current dipoles located in different layers contribute to the macroscopic oscillation 12,[28][29][30][31][32] . Conversely, it is believed that theta oscillations are robustly synchronized within each layer across the anatomical extent of the hippocampus 28,[32][33][34] , despite some early evidence to the contrary 26 .…”

Volume conduction and EEG measurements within the brain: A quantitative approach to the influence of electrical spread on the linear relationship of activity measured at different locations

“…When recording such a strong remote source with two electrodes against a reference this may result in a large in-phase component in the simultaneous records. In order to distinguish this situation from one with two phase-locked sources in the surroundings of both electrodes, the phase and amplitude relations between the signals in the frequency range of interest can provide more information since volume conduction is a process giving rise to constant phase and continuous decrease of amplitude as a function of distance from the neuronal source (Winson 1974(Winson , 1976Bland et al 1975;Feenstra and Holsheimer, in preparation).…”

Generation of theta activity (RSA) in the cingulate cortex of the rat

“…During arousal they found regular theta rhythm in the hippocampus, but irregular theta activity in the cortex of the awake rabbit. Winson (1974) reported that both intermittent theta or absence of theta in the cortex could be found during regular hippocampal theta rhythm in the awake rat. These findings suggest that theta field potentials in parts of the cortex overlying the hippocampal complex may not be considered solely the result of volume conduction from a hippocampal source, i.e., there is a possibility that hippocampal and cortical theta have different neuronal sources.…”

“…Although without specifying the cortical areas from which it was recorded, Artemenko (1972), Winson (1974), Bland and Whishaw (1976), and Gerbrandt et al (1978 described cortical theta to be isomorphic with theta in the neighboring part of the hippocampus, the amplitude decreasing toward the cortical surface. Cortical theta would thus be accounted for in terms of volume conduction theory, since a stationary neuronal source in a purely resistive medium causes a field potential, the amplitude of which decreases with increasing distance from this source without phase shift (Holsheimer and Feenstra 1977).…”