An allometric analysis of the frequency of hippocampal theta: the significance of brain metabolic rate.

The dominant frequency of hippocampal rhythmic slow activity (RSA) is known to differ among species, even under similar experimental conditions. The cause of these species differences has not yet been identified. In this paper it is shown that RSA frequency is allometrically related to brain size for the 9 mammalian species for which data are available. It is further shown that the relationship between brain size and RSA frequency is similar to the relationship between brain size and specific brain metabolic rate. Based on these and other relationships, it is suggested that differences in the firing frequencies of the neuronal pacemakers underlying the generation of RSA reflect differences in specific brain metabolic rate, both within and among species.