Memory Traces of Pain in Human Cortex

Distinct brain regions process sensory discriminative and affective components of pain; however, the role of these areas in pain memory is unknown. This event-related study investigated the short-term memory for sensory features of cutaneous heat pain using a delayed-discrimination paradigm and functional magnetic resonance imaging. During memory trials, subjects discriminated the location and intensity of two painful stimuli presented sequentially to the right hand. Control trials comprised the same sequence of stimuli and motor responses but required no delayed discrimination. Stimulus-evoked activity for memory and control trials was generally indistinguishable within the network of regions normally responsive to experimental pain [i.e., the primary somatosensory cortex/posterior parietal cortex (SI/PPC), secondary somatosensory cortex (SII), and anterior insular cortex (aIC)]; these data confirm the painful nature of the stimuli and the similar levels of attention and stimulus encoding engaged during the two randomly presented trial types. Memory-specific activity, assessed by contrasting the interstimulus interval in memory and control trials, was observed in SI/PPC and aIC but not in SII. We propose that SI/PPC plays a role in the short-term retention of spatial and intensity aspects of noxious stimuli and that aIC activation during memory trials is consistent with the integration of sensory and cognitive (attention, awareness, salience, and memory) components of pain perception. The absence of memory-specific anterior cingulate cortex activation, generally associated with pain unpleasantness, suggests that remembering affective aspects of the stimuli was not required during performance of the sensory delayed-discrimination task.