Short-Term Nociceptive Memory: Reduced Discriminability and Multiple Encoding Biases

Distortions in pain memory carry important clinical implications, yet the processes underlying retention of nociceptive information remain incompletely understood. This study examined how the intensity of painful somatosensory inputs is maintained in memory over different intervals.

Twenty-five participants received pairs of nociceptive or non-nociceptive electrical stimuli at varying inter-stimulus intervals (3, 8, 13, 18 s), and judged whether the second stimulus was of higher, equal, or lower intensity than the first.

In accordance with Weber-Fletcher Law, perceptual discriminability was lower in the nociceptive condition, leading to a decreased accuracy despite comparable confidence ratings. Memory performance declined with temporal delay similarly for both modalities. Accuracy increased when the second stimulus was more intense than the first. For nociceptive stimuli only, accuracy deteriorated disproportionately when the second stimulus was weaker, suggesting a directional encoding bias specific to pain. When errors occurred, participants overestimated the intensity of the second stimulus, a bias more pronounced for nociceptive stimuli. Such overestimation was linked to memory encoding and disappeared when participants rated stimuli without memory demand.

Short-term memory for nociceptive stimuli proved less accurate, more directionally biased, and more prone to overestimation than for non-nociceptive inputs. While this performance gap is largely explained by reduced perceptual discriminability at pain intensities, modality-specific distortions point to additional constraints imposed by nociceptive processing on memory encoding and maintenance.

This study provides psychophysical evidence for differences in short-term memory retention of nociceptive versus non-nociceptive sensory input, with implications for understanding pain memory distortions in clinical contexts.