Comparative cerebral responses to non-painful warm vs. cold stimuli in man: EEG power spectra and coherence.

Aims: The cerebral processing of painful thermal (heat/cold) stimulation have been extensively studied, but little is known about cerebral activation to non-painful warm and cold stimuli. This study aimed to investigate the comparative EEG effects of warm vs. cold stimulus in man.
Materials and Methods: The left nondominant hands of 13 healthy male subjects were stimulated by non-painful warm (40-43 degrees C) and cold (12-15 degrees C) water. The somatic sensations were continuously assessed with an analogue visual scale device. EEG data (32 channels) recorded before, during and after the warm and cold stimulations were analysed quantitatively.
Results: No significant difference in intensity of sensation was found during warm and cold stimulations. Different patterns of EEG activity were superimposed on the similar background of EEG activation during and after warm and cold stimulations. Significant decrease of theta activity in contra-stimulus frontal region was observed during cold stimulation rather than warm stimulation. EEG power spectra in theta, alpha-1 and alpha-2 bands significantly increased after cold stimulation compared to baseline. EEG coherence in delta, alpha-1 and alpha-2 bands significantly increased in the contra-stimulus hemisphere during stimulations.
Conclusion: This suggests that similar neural networks may process somatic warm and cold sensory inputs differently and the differential EEG patterns may be encoded by the qualities of thermal stimuli.