Laboratory of Neurophysiology and Bioinformatics, Graduate School of Information Sciences
Tohoku University, Sendai 980-77, Japan
Department of Psychology, Tokyo Metropolitan Institute for Neurosciences
Fuchu 183, Japan
t is important to clarify a mechanism of global modulation of the brain, since the brain always behaves as a whole. Basic endogenous aspects of the mechanism must be reflected in slow neuronal dynamics during sleep; because, (I) during sleep the brain is most isolated from
the external environment and is essentially controlled by endogenous signals, ands (2) sleep process is a phenomenon spreading all over the brain and is slowly changing in the brain.
It was first discovered in the mesencephalic reticular formation of a cat, that single neuronal activities had a white spectrum (a flat power spectral density function) during a steady state of slow wave sleep for a very low frequency range of 0.01 - 1.0 Hz, and had a 1/f spectrum (a power spectral density function inversely proportional to frequency f) during REM sleep for almost the same frequency range**).
The similar phenomenon of the neuronal dynamics-transition between the two sleep states was commonly found in various regions of the brain such as the thalamus, the neocortex, and the limbic system, which we call "executive systems" of the brain.
To interpret the common dynamics-transition in the executive systems, pharmacological experiments were performed using a blocker of serotonin synthesis, serotonergic receptor's agonist and cholinergic receptor's antagonist.
Based on the results of the experiments, we successfully simulated the dynamics-transition by using a neural network model including a common inhibitory input and mutually independent random perturbations, respectively introduced to mimic biasing influences of modulatory systems and various noise sources consisting of rapidly fluctuating components of cholinergic and noncholinergic drives. A manipulation of either the common inhibition or the variance of the random perturbations produced the dynamics-transition similar to what was observed in the executive systems of the brain.
Conclusions: (1) Slow wave sleep and REM sleep have the white and the 1/f slow neuronal dynamics in executive systems, respectively. (2) Aminergic and cholinergic modulatory systems are deeply related to the dynamics-transition. (3) The possible mechanism looks like one from the network origin with variable global modulation.
**) Yamamoto, M. et al., Brain Res. 366, 279-289 (1986)
