Pain perception and response: Central nervous system mechanisms

Although several decades of studies have detailed peripheral and ascending nociceptive pathways to the thalamus and cerebral cortex, pain is a symptom that has remained difficult to characterize anatomically and physiological ly. Positron emission tomography (PET) and functional magnetic imaging (fMR I) have recently demonstrated a number of cerebral and brain stem loci resp onding to cutaneous noxious stimuli. However, intersubject variability, bot h in the frequency and increased or decreased intensity of the responses, h as caused uncertainty as to their significance. Nevertheless, the large num ber of available imaging studies have shown that;many areas with recognized functions are frequently affected by painful stimuli. With this evidence a nd recent developments in tracing central nervous system connections betwee n areas responding to noxious stimuli, it is possible to identify nocicepti ve pathways that are within, or contribute to, afferent spinothalamo-cortic al sensory and efferent skeletomotor and autonomic motor systems. In this s tudy it is proposed that cortical and nuclear mechanisms for pain perceptio n and response are hierarchically arranged with the prefrontal cortex at it s highest level. Nevertheless, all components make particular contributions without which certain nociceptive failures can occur, as in pathological p ain arising in some cases of nervous system injury.