Pupillometry and memory: External signals of metacognitive control

For centuries, researchers have examined the dynamics of pupil dilation and constriction, as it is well known that pupil size is affected by many physical stimuli, including ambient lighting and temperature (e.g., Fontana, Dei moti dell’iride, 1765). Less well known is that the pupils also dilate in response to nonphysical stimuli, such as emotions and thoughts. These latter changes, phasic pupillary reflexes, follow the onset of cognitive processing. The neurophysiological mechanisms of these reflexes have been attributed to autonomic nervous system activity, including parasympathetic nervous system areas that are controlled by the locus coeruleus–norepinephrine (LC-NE) system of the brain. Tight correspondences between single-cell firing rates in the monkey LC-NE system and concomitant pupil dilation/constriction suggest that the LC-NE system is critically involved in controlling phasic pupillary changes. Relevant to students of memory, the LC-NE system is also involved in memory consolidation, and is active during retrieval. Animal models reveal close correspondence between accurate learning and memory and the involvement of the autonomic system, and stimulation of the vagus nerve is associated with memory formation and consolidation. Because of the connection between pupillary reflexes and neuroanatomical structures related to memory, researchers have recently used pupillometry to investigate questions of human memory. In this chapter, we review that evidence, and discuss phasic pupillary reflexes in relation to subjective feelings of memory, including feelings of future memory during learning. Such findings suggest a tight connection between pupillary changes and self-regulated cognition, and point toward new approaches to study the motivation–cognition interface.