Eye Tracking, Cortisol, and a Sleep vs. Wake Consolidation Delay: Combining Methods to Uncover an Interactive Effect of Sleep and Cortisol on Memory

The overall goal of the following experiment is to determine whether there is an interactive effect of sleep and cortisol on memory consolidation or on the link between over detention, adding coding, and subsequent memory. This is achieved first by having participants salivate on an oral swab to assess their resting cortisol level prior to encoding stimuli to encode the stimuli. Participants judge whether they would hypothetically approach or back away from scenes consisting of either a negative or neutral object superimposed on a plausible neutral background.

Their eye gaze is tracked as they view these scenes so that the amount of time spent looking at the objects within the scenes can be measured next. After a 12 hour delay consisting of either a full night of sleep or an equivalent amount of time spent awake participants'memory of the individual scene components is tested. The results show that higher resting cortisol is correlated with enhanced memory for negative objects, but only if sleep occurs during the consolidation interval.

Further, for those with higher resting cortisol, there is an enhanced relation between looking time at encoding and subsequent emotional memory. An effect that is, again, dependent on the sleep occurring during the consolidation interval. The main advantage of this technique is that we could examine the interactive effects of sleep and cortisol on emotional memory building upon prior work, showing that these two variables separately affect memory performance.

This method can help answer key questions in the fields of cognitive psychology and cognitive neuroscience. Here we use this combination of methods to show that elevated cortisol may tag attended objects as important to remember during encoding, thereby enabling sleep to selectively strengthen that salient information during the consolidation interval. To begin, recruit participants as described in the accompanying text protocol schedule.

Sleep participant in coding sessions between seven and 10:00 PM and the retrieval sessions 12 hours later, following a full night of sleep in the laboratory schedule. Wake participant in coding sessions between seven and 10:00 AM and the retrieval sessions 12 hours later, following a full day of wake fullness schedule the morning short delay participants between seven and 10:00 AM and the evening short Delay participants between seven and 10:00 PM Test the participants 20 minutes after encoding. If full random assignment is not possible, ensure that participants do not differ in age or in scores on the morning ness.

Eveningness questionnaire, Beck depression inventory, Beck anxiety inventory, or the amount of sleep obtained on the night before retrieval. If focusing on emotional memory as in the present study, select scenes composed of a negative or neutral object placed on a neutral background, ensure that all emotional stimuli have been previously rated for valence and arousal. Randomly intermixed the negative and neutral scenes between two 10 minute blocks, which will allow the participants to have a short break to rest their eyes in between.

Ensure that participants have not engaged in any physical activity, consumed anything besides water, smoked or brushed their teeth for two hours prior to encoding, and ensure that they have not had water for at least 15 minutes prior to encoding. Immediately prior to encoding. Instruct participants to rinse their mouths with approximately one ounce of water.

Remind the participants not to swallow the water to avoid sample dilution. Next, instruct participants to salivate on an oral swab for two minutes. Then ask participants to place the oral swab in a swab storage tube and store the swabs at zero degrees Fahrenheit until analyzed.

First, ask the participants to sit with their chin on the chin rest and to place their forehead up against the bar. Make adjustments to the chair, height and chin rest to ensure that the center of the screen is aligned with the participants'eyes. Ensure that participants are wearing contacts rather than glasses and that they are not wearing eye makeup.

Perform a calibration task to ensure that the eye tracker is accurately tracking the participant's gaze within one degree of accuracy. Ask participants to indicate via mouse click whether they would approach or back away from the presented scene if they were to encounter it in real life. Once the participant is ready to begin, start the task and press the record button.

Allow participants to have a short, self-determined break of 10 to 60 seconds between blocks and ask them to indicate when they are ready to continue. Then use software to draw areas of interest or AOIs to measure their attention to the negative or neutral object within the scene. After drawing the AOIs, calculate the proportion of time participants look at the A OI relative to the rest of the scene.

Ensure that the delay length between encoding and retrieval for the sleep and wake conditions and the delay length for the two control conditions are equal respectively for sleep. Participants ensure that the 12 hour delay includes eight hours of sleep. Conversely, ensure that the wake participants do not sleep or nap during the interval.

Ask the morning and evening short delay participants to remain in the laboratory during their 20 minute delay. Inform that they may do as they please during this time, provided that they do not nap. Following the delay period, administer the recognition memory test.

Ask participants to indicate whether the displayed stimulus is old or included in a previously studied scene or new and not previously studied by pressing corresponding keys on a keyboard. This graph demonstrates the effect of cortisol on memory performance for negative objects. Standardized levels of cortisol and memory performance for negative objects were directly related in sleep participants, but not in wake participants.

A similar but weaker pattern was observed when analyzing the effect of standardized cortisol levels on memory performance for neutral objects looking time was calculated as the proportion of time spent looking at the object within the scene relative to the total scene viewing time, A score was then computed to reflect the difference in looking time between subsequently remembered and subsequently forgotten objects, or the difference in looking time as a function of later memory. Resting cortisol marginally predicted the difference in looking time as a function of later memory in the sleep group, but not the wake group for negative objects. The group by cortisol interaction was significant.

Following this procedure, it was possible to determine that the facilitative effects of preem coding cortisol on emotional memory following delays of at least 24 hours, including sleep, may be due to interactions between cortisol and sleep dependent consolidation processes. After watching this video, it should be clear that combining methods that are typically used independently, such as eye tracking, cortisol assays, and testing memory across sleep versus wake delays will help researchers better understand the complex interactions between variables that affect cognition.