By: Neha Kakkar

 Observations that sleep deprivation affects temporal memory were first made around 50 years ago by Morris, Williams and Lubin.  Psychological tests sensitive to sleep deprivation have usually been administered to sleep deprived volunteers, previously well trained in the test procedures.  However, these tests are simple and straightforward, but by the time they are tested on the sleep deprived people, they become tedious boring.

 In 1977, Wilkinson suggested that boredom may be the key to a test’s sensitivity to sleep deprivation.  He emphasized the point that ‘sleep deprivation reduces the non-specific arousal level of the body, but has no specific effects”.  This study focuses on the more specific effects of sleep deprivation on temporal memory, rather than the non- specific arousal effects.

 Between subjects  4 conditions  Control non-sleep deprived with placebo(Cp,n=10)  Control non-sleep deprived with caffeine (Cc, n=10)  Sleep deprived with caffeine (SDc, n=10)  Sleep deprived with placebo (SDp, n=10)  35hrs without sleep   Caffeine and placebo were given double blind.

 N=40 (20 females, 20 Males)  Mean Age:23.4yrs  Volunteers were screened to exclude smokers, heavy drinkers and those with sleep or medical problems such as insomnia.  All were moderate consumers of caffeine (100mg – 400mg)  Normal range (<10) of the Epworth Sleepiness Scale

 Caffeine is not known to improve performance in alert, non-sleep deprived subjects undergoing short-duration tests. ◦ Control groups allowed to check this. 350mg Anhydrous caffeine dissolved in 200ml decaffeinated coffee given in a divided dose (200mg:16:45, 150mg:18:45) Placebo: decaffeinated coffee only

 Task was explained a day prior to the study but were not allowed to practice  All groups tested between 7:30 to 8:30  Temporal memory for faces task: based on colour photographs of unfamiliar faces.  Two sets of photographs were presented with a delay of 5 min between the presentations List A: 12 faces List B: 12 faces

 After both sets, another presentation of random 48 faces including 24 previously presented faces. - For each one, asked whether they had seen the photo before (recognition) and also if it was part of List A or B (recency)

 Two-way ANOVA (sleep condition x caffeine)  Three-way ANOVA (sleep condition x caffeine x accuracy)  Recognition  No significant effects of sleep condition F(1,36)=0.16  No significant effects for caffeine F(1,36) = 0.46  No interaction F(1,36) = 1.57

Recency Significant Main effect of sleep condition F(1,36)=25.62, p<.005 Significant interaction (sleep condition x caffeine interaction) F(1,36) = 4.26, p<.05 No main effect of caffeine F(1,36) = 0.74

Accuracy Significant main effect for accuracy F(1,72)=16.7,p<.005 All groups were more confident about being correct when judging responses that were right Significant effect for sleep condition, F(1,72)=13.63, p<.005 Sleep deprived participants were more confident than control about being correct for both right and wrong responses. Sleep deprived individuals were significantly more confident when they were wrong.

 Improved alertness by caffeine is clearly evident.  SDc group was more alert than SDp group.  Sleep deprivation did not significantly affect the recognition of faces, it did produce significant impairment of the temporal memory (recency component : List A or B)  This suggests that sleep deprivation was having a specific effect on temporal memory, other than simply through a generalized reduction in arousal.

 Even though caffeine resulted in reduction in sleep for SDc group, they still performed worse than both control groups. Temporal memory component of this faces test seems to rely on the integrity of the PFC (Daum et. al, 1996) Patients with damaged PFC are impaired at the recency aspect of the task rather than with the recognition component (Daum et. al, 1996).

 Whether or not the present findings indicate sleep deprivation affects the PFC is a matter of debate ◦ It could be possible that the recognition component of the face test may simply be less difficult and demanding than the recency part for the sleep deprived individual.  Limitation: no agreed way of measuring task difficulty  Other sleep deprivation studies using neuropsychological testing indicate that PFC maybe prone to impairment during sleep loss (Harrison & Horne, 1996).

 With present findings,, it may not be clear whether the effects of sleep deprivation relate to a general problem with source memory than more specifically to temporal memory.  To determine this, one would need to look at the other aspects of the encoding stage ex: where, who, if and when.

Strengths:  Very easy to read and understand  Good display of results Weakness:  Not much interpretation of the results, short discussion section Further experiments:  Use fMRI or PET scan to compare the brain activations of sleep deprived and control participants