Nociceptive responses of anterior cingulate cortical ensembles in behaving rats

To confirm the role of anterior cingulated cortices (ACC) in the coding of pain affect by exploring the neural ensemble coding pattern within the anterior cingulate cortex in behaving rats with a multichannel recording technique.

In five adult male Sprague-Dawley rats, two arrays of eight stainless steel microwires were bilaterally implanted into ACC. Noxious radiant heat stimulation was applied to the tail, bilateral fore-paws and hind-paws of freely moving rats. Neuroelectric signals were obtained from the microwires and sent to a multichannel recording device via cables and connectors. The time stamps of neuronal activities were stored on a personal computer for off-line analysis.

Noxious heat stimuli evoked predominantly excitatory and sustained neural activity within ACC, reflecting the processing of pain unpleasantness; pain-related anticipatory responses could be seen near the stimulation start, indicating the behavioral preparation for escape; ACC neurons had broad receptive fields by showing quite similar pain-related responses to stimuli on either side of the hind-paw, suggesting that they are not eligible for the localization of a stimulus.

ACC has played a major role in processing the affective-motivational aspect of pain.