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The motor cortex of 10 healthy subjects was stimulated by transcranial magnetic stimulation (TMS) before and after ethanol challenge (0.8 g/kg resulting in blood concentration of 0.77 +/- 0.14 ml/liter). The electrical brain activity resulting from the brief electromagnetic pulse was recorded with high-resolution electroencephalography (EEG) and located using inversion algorithms. Focal magnetic pulses to the left motor cortex were delivered with a figure-of-eight coil at the random interstimulus interval of 1.5-2.5 s. The stimulation intensity was adjusted to the motor threshold of abductor digiti minimi. Two conditions before and after ethanol ingestion (30 min) were applied: (1) real TMS, with the coil pressed against the scalp; and (2) control condition, with the coil separated from the scalp by a 2-cm-thick piece of plastic. A separate EMG control recording of one subject during TMS was made with two bipolar platinum needle electrodes inserted to the left temporal muscle. In each condition, 120 pulses were delivered. The EEG was recorded from 60 scalp electrodes. A peak in the EEG signals was observed at 43 ms after the TMS pulse in the real-TMS condition but not in the control condition or in the control scalp EMG. Potential maps before and after ethanol ingestion were significantly different from each other (P = 0.01), but no differences were found in the control condition. Ethanol changed the TMS-evoked potentials over right frontal and left parietal areas, the underlying effect appearing to be largest in the right prefrontal area. Our findings suggest that ethanol may have changed the functional connectivity between prefrontal and motor cortices. This new noninvasive method provides direct evidence about the modulation of cortical connectivity after ethanol challenge.

Introduction The brain spontaneously generates complex patterns of oscillatory activity whose dynamic signature is poorly understood. Identifying hidden structures in the electrophysiological time series could yield important insights into the function and mechanisms of large-scale neuronal interactions. Self-organized criticality (SOC) provides a general theoretical framework of how complex systems can evolve to a non-equilibrium state characterized by power-law scaling behavior [l]. This statistical property of the critical state stems from a non-linear process creating transient spatio-temporal correlations at wide scales and lends the system susceptible to change. We explore the possibility that the dynamical fingerprint of criticality in a family of complex systems is shared by oscillations in the human brain. Methods Spontaneous electrical brain activity from 8 normal subjects (aged 20-30 years, 1 female) was recorded using a whole-scalp magnetometer with 122 planar gradiometers. The subjects were seated in a magnetically shielded room and instructed to relax with eyes either open or closed in two separate 20-minute recording sessions. The measurements were replicated in 4 subjects, giving 12 data sets for each condition. The time-varying signal amplitude of narrow frequency bands was estimated by means of wavelet analysis. We focussed the analysis on the 8-13 Hz frequency range due to the high signal-to-noise ratio of the alpha rhythm. Results Wavelet transformation of the time series revealed amplitude fluctuations on wide time scales (Fig. 1). To detect power-law temporal correlations, characteristic for scale-invariant systems far from equilibrium, we employed the detrended fluctuation analysis [2]. The outcome was a remarkably invariant and persistent scaling behavior across subjects and conditions (Fig. 2), indicating a lack of ‘typical’ time scales for the duration and recurrence of oscillations. Least-squares fits in double logarithmic coordinates yielded self-similarity parameters