Observations On Operant Conditioning And Single Unit Activity In Prefrontal Cortex Of Rhesus Monkeys During Acupuncture

Liu Jinlong, Han Xiangwen, Jin Wenlong, Department of Physiology, Guangxi Medical College.

Qi Dailin, Zhou Huiju, Department of Physiology, Guiyang Medical College.

Hou Gangxing, Wang Zouqing, Yang Congguo, Liu Zuozhou, Department of Physiology, The Third Medical College of PLA.

In the present study an attempt was made to examine whether the prefrontal cortex is involved in acupuncture analgesia. Experiments were carried on 12 conscious, movable adult monkeys (Macaca mulatta), weighing 3.5~5 Kg. The animals were trained in a restrained chair to pull a lever to escape noxious electrical stimulation of the tail. The single unit activity was recorded in the meantime with a tungsten microelectrode in dorsolateral prefronal cortex. A total of 111 units were recorded from pre-arcuate, post-arcuate and principal sulcus areas. Spontaneously active units were found in all the areas explored, but their discharge rates varied in any given region. Some units showed irregular impulses at mean frequencies as low as 0.25 Hz, whereas others had rates of 70 Hz or higher, but the majority (81.9%) fired at frequencies within a range of 1 ~ 10 Hz. A few units (17.6%) fired in bursts of 2~20 impulses with frequencies as high as 600~800 Hz. For most units, spontaneous rate of discharge significantly increased 50~1000% under the influence of noxious stimulation. In some cases, diphasic responses, i.e. a brief period of decrease in firing rate followed by a longterm increment, or a brief increase followed by a decrement, could also be seen. As to the relation of the changes of firing rate to the action of lever-pulling, a wide diversity of spike activity patterns existed in different units: some units decreased or increased their firing rate prior to the lever-pulling action and others failed to respond until the action started. During electro-acupuncture, the lever-pulling threshold, which was used as an indicator of pain, was increased within 10~30 min, and the spontaneous firing rate also increased 50~800% in most of the units, but there was no relation to their level of background activity. At that time, the effect of noxious stimulation was also weakened or even reversed; nevertheless, the changes of unit firing rate and the elevation of lever-pulling threshold sometimes showed no consistency. Similar results were also obtained from two rhesus monkeys paralyzed by flaxedil under acute conditions. After the application of dolantin, the threshold of operant avoidance and the spontaneous unit discharge frequency both increased, and the response of some units to noxious stimulation was weakened or reversed. It was suggested that the dorsolateral prefrontal cortex might play a role in the psychological aspect of acupuncture analgesic effect.