Effect of intranasally administered cholecystokinin on encoding of controlled and automatic memory processes

The neuropeptide cholecystokinin (CCK) is present in abundance in the central nervous system, where it is involved in the regulation of a wide range of functions. It also takes part in the modulation of memory processes, but its effect on human memory systems and processes is not yet well understood.

The present experiment was conducted to examine the influence of CCK when present during encoding on later controlled and automatic recognition memory processes in humans.

A version of the process dissociation procedure was used to separate the contributions of controlled and automatic memory processes to participants' recognition memory performance. Data were analyzed within a multinomial modeling framework. Participants (N = 64) received either 40 microg CCK-8S or placebo intranasally. The learning and test phases began 30 min after substance application. Behavioral, physiological, and self-report control variables were measured at three points of time during the experiment.

Compared to placebo, CCK increased the automatic, familiarity-based recognition memory component, while the parameter representing controlled, retrieval-based processes did not differ between groups. Also, in the exclusion condition of the test phase, the guessing parameter was reduced by CCK. None of the control variables were affected by the peptide.

This result-the enhancement of the automatic recognition memory component when CCK is applied before encoding (and thus present during encoding and retrieval)-complements earlier results indicating that CCK decreases controlled, recollection-based recognition memory when applied during consolidation. The possible neuronal systems and processes mediating these effects are discussed.