Inspector (Ret.) Chris Butler

New Research Improves Understanding of the Relationship between Sleep and Memory Consolidation

Decades of research on memory formation has advanced our understanding of how we perceive events, the role of heuristics and context cues – how we see what we expect to see even if the anticipated stimulus was not present, and how we can not ‘see’ what we don’t expect even though the stimulus was right in front of us. Researchers have also studied memory errors such as confabulation – how our brains will fill in gaps in our memory based upon the influence of our implicit bias and ‘mental model’ of what must have occurred (whether it actually did or not).


What about confidence? Does a person’s level of confidence or assuredness of their memory actually relate to the accuracy? This is an important question because judges and juries have been, and still continue to be swayed by their perception of the confidence, or conversely, lack of confidence of the witness – whether a professional witness such as a police officer or a civilian witness.

Several researchers have explored the relationship between observer confidence and memory accuracy. One of the most recent and relevant studies (Beehr, Ivanitskaya, Glaser, Erofeev and Canali) explored the accuracy of police officer’s memory and compared those memories to the officers’ level of confidence. It was determined that there was no relationship between officer confidence and how accurate their memories were. In fact, several officers who reported not being very confident in their memory actually had more accurate memories of many of the ‘confident’ officers.[1]

Acute Stress, Memory & Sleep

With respect to the occupation of law enforcement, one of the pressing questions and current debates is how an acute stress event (such as an officer involved shooting) might impact an officer’s memory formation. The impact of acute stressors on officer and witness memory has been a specific area of burgeoning research in recent years. Some research has demonstrated that stressful events lead to poorer memory of overall details[2] while other research has clearly demonstrated enhanced memory for specific, salient portions of the incident.[3] A lack of understanding of these critical issues has resulted in officers being accused of being deceitful, being charged criminally and sometimes convicted largely because of the officers inability to recall significant details for portion of the event. This, despite the fact that the memory research conclusively demonstrates a relationship between high levels of cognitive anxiety and physiological activation (‘fight or flight response) and a catastrophic drop in memory performance.[4][5][6]

Perhaps one of the most significant issues facing investigators tasked with interviewing police officers after an acute stress incident, such as a shooting, is should the officer be interviewed immediately afterwards, or should the interview be delayed. The function of the interviewer ought to be to obtain the most accurate possible memory recall from the witness officer while inducing the fewest possible memory errors. Therefore, not only is the type of interview critical (and I would argue that the balance of evidence-based research supports the Cognitive Interview technique – but that discussion is for another time), but also the timing of the interview is critically important.

Many large municipal agencies that I am familiar with have policy on ensuring the officer is provided a period of rest – typically at least one full sleep cycle if not more. For example, the IACP OIS Guidelines state that their Psychological Services Section recommends delaying interviews from 48-72 hours “in order to provide the officer with sufficient recovery time to enhance recall”[7] In a similar vein, in April of 2017, the Wisconsin Department of Justice published their General Investigative Guidelines for Officer-Involved Death Investigations which states that following a critical incident “Officers may be allowed to go home and sleep and wait 24-72 hours after the incident to give a formal statement.”[8]

The practice of delaying the interview to allow police officers to form the most accurate ‘consolidated’ memories, while supported by several research studies, is not without controversy, especially by certain special interest groups in North America. This controversy continues to create ‘fog’ despite the fact that the research literature on memory formation demonstrates a strong correlation between sleep (specifically, NREM or ‘slow wave’ sleep) and memory accuracy.

Now, new research led by Dr. Thomas Schreiner, of the University of Birmingham’s School of Psychology along with fellow researchers at the Donders Institute in Holland has further enlightened our understanding of the effect of sleep on memory formation and consolidation.[9] This research, just reported (October 10, 2018) in Neuro Science News[10], explored, for the first time ever, the functional neural mechanisms that cause consolidation during sleep. The researchers recorded the specific neural pathways of the study volunteers as they were sleeping, and they discovered “the neural activity we recorded provides further evidence for how important sleep is to memory and, ultimately, for our well-being.”

This research is aligned with previous research that shows a strong role of NREM (Non-Rapid Eye Movement) sleep and long-term memory consolidation in the hippocampus. While the researchers did not explore the effect of acute stress on memory formation, the results of their study further reinforce the understanding of the vital role between ‘slow wave’ or theta sleep and the consolidation of long-term memory.

The investigative practice of delaying the full interview with subject officers until after a sufficient opportunity for at least one full NREM sleep cycle to occur remains strongly supported by the research.

That is, if your goal is to obtain the fullest, most accurate memory recall!


[1] Beehr, Ivanitskaya, Glaser, Erofeev and Canali; “Working in a Violent Environment: The Accuracy of Police Officers’ Reports about Shooting Incidents”; Journal of Occupational and Organizational Psychology; 77, 217-235; (2004).

[2] Kassin, Ellsworth, Smith; “The General Acceptance of Psychological Research on Eyewitness Testimony; A Survey of Experts; American Psychologist; 44, 10879-1098; (1989).

[3] Burke, Heuer & Reisberg; “Remembering Emotional Events”; Memory and Cognition; 20,277-290; (1992).

[4] Deffenbacher, K.A.; “Effects of Arousal on Everyday Memory”; Human Performance; 7,141-161; (1994).

[5] Pigott, Brigham & Bothwell; “An Exploratory Study of Personality Differences in Eyewitness Memory”; Journal of Social behavior and Personality; 2, 335-343; (1987).

[6] Deffenbacher, Bornstein, Penrod and McGorty; “A Meta-Analytic Review of the Effects of High Stress on Eyewitness Memory”; Law and Human Behavior; Vol. 28, No. 6; (2004)

[7] International Association of Chiefs of Police “Officer-Involved Shootings: A Guide for Law Enforcement Leaders”; Washington, DC: Office of Community Oriented Policing Services; (2016).

[8] General Investigative Guidelines for Officer-Involved Death Investigations”; Wisconsin DOJ; April (2017).

[9] Schreiner, Doeller, Jensen, Rasch and Staudigl; “Theta Phase-Coordinated Memory Reactivation Reoccurs in a Slow-Oscillatory Rhythm during NREM Sleep”; Cell Reports; 25, 296-301; (October 9, 2018).

[10] Memory Brainwaves Look the Same in Sleep and Wakefulness; Neuro Science News; retrieved October 10, 2018 at