THE CEREBRAL RESPONSE TO ELECTRICAL STIMULI IN THE ESOPHAGUS IS ALTERED BY INCREASING STIMULUS FREQUENCIES

Recording of cerebral evoked responses (EP) allows the assessment of v isceral afferent pathways and gut-brain communication, but the optimal stimulation parameters remain to be established. The present study de termined the optimal stimulation frequency of electrical stimulation o f the oesophagus to elicit EP responses. In 13 healthy male volunteers (24.1 +/- 5.9 years), a 5mm stainless-steel electrode was placed in t he distal oesophagus for electrical stimulation (ES). EP were recorded from 21 scalp electrodes placed according to the 10/20 International system. ES (15 mA, 200 mu s) were delivered in repeated series of 24 s timuli. Stimulus frequency was randomly altered in different series us ing a pseudologarithmic range (0.1, 0.2, 0.3, 0.5, and 2 Hz). Two seri es of stimuli were applied using each stimulation frequency. Two-dimen sional topographic brain maps were created using interpolation techniq ues at each stimulation frequency. With increasing stimulus frequency, a significant and progressive decrease of EP amplitudes was observed between frequencies of 0.2 Hz and 1.0 Hz (P1/N2: 7.6 +/- 1.2 vs 1.4 +/ - 0.3 mu V, N2/P2: 17.2 +/- 1.7 vs 4.6 +/- 0.4* mu V, P2/N3: 6.9 +/- 0.7 vs 4.2 +/- 0.5 mu V; * = P < 0.05). In addition, there was a sign ificant shortening of the mean peak latency of the intercalated P2 pea k (P < 0.0005), with a similar trend for the P3 peak (P < 0.06), with increasing stimulus frequency from 0.2-1.0 Hz. Topographic brain maps localized the maximal early peaks (NZ,P1,N2) in the paracentral cortic al region (C3, Ct, C4), whereas the later peaks (P2 to P3) were symmet rically spread over the centroparietal and temporal regions (Ct, Pt, T 5, T4). There was no difference in the cortical location of maximal EP amplitudes with increasing stimulus frequency In conclusion, there is a clear relationship between stimulus frequency and amplitude of EP, suggesting rapid attenuation of the cerebral autonomic neural response s with increased electrical stimulation frequency. The effect of incre ased frequency on peak latencies suggests an alteration of stimulus pr ocessing in the thalamocortical region due to an altered perception of stimuli. Early EP peaks originate from basal structures of primarily the dominant hemisphere, while later peaks are localized in centropari etal cortical regions.