Kosuke Kaida

Dopamine d2-like receptor activation wipes out preferential consolidation of high over low reward memories during human sleep

Memory formation is a selective process in which reward contingencies determine which memory is maintained and which is forgotten. Sleep plays a pivotal role in maintaining information for the long term and has been shown to specifically benefit memories that are associated with reward. Key to memory consolidation during sleep is a neuronal reactivation of newly encoded representations. However, it is unclear whether preferential consolidation of memories associated with reward requires the reactivation of dopaminergic circuitry known to mediate reward effects at encoding. In a placebo-controlled, double-blind, balanced crossover experiment, we show that the dopamine D2-like receptor agonist pramipexole given during sleep wipes out reward contingencies. Before sleep, 16 men learned 160 pictures of landscapes and interiors that were associated with high or low rewards, if they were identified between new stimuli at retrieval 24 hr later. In the placebo condition, the participants retained significantly more pictures that promised a high reward. In the pramipexole condition, this difference was wiped out, and performance for the low reward pictures was as high as that for high reward pictures. Pramipexole did not generally enhance memory consolidation probably because of the fact that the dopaminergic agonist concurrently suppressed both SWS and REM sleep. These results are consistent with the concept that preferential consolidation of reward-associated memories relies on hippocampus-driven reactivation within the dopaminergic reward system during sleep, whereby during sleep reward contingencies are fed back to the hippocampus to strengthen specific memories, possibly, through dopaminergic facilitation of long-term potentiation.

Pro-environmental behavior correlates with present and future subjective well-being

This paper reports structural associations between psychological states, pro-environmental behavior, and present and future subjective well-being. A mailed questionnaire surveyed residents in Stockholm County, Sweden, to gather data on pro-environmental behaviors in water and energy saving at home, universalism and intrinsic satisfaction as motivational factors, and present and future subjective well-being. Results of path analysis suggest that: (1) Psychological factors (i.e., universalism, frugality, and participation categories of intrinsic satisfaction) correlate with pro-environmental behavior; (2) pro-environmental behavior could enhance not only present subjective well-being but expectations of future subjective well-being; and (3) expectations of future subjective well-being are negatively associated with current pro-environmental behavior. An important implication of this study is that expectation of better future subjective well-being may not always facilitate pro-environmental behavior. These results suggest that psychological factors both as antecedents and consequences play a significant role in building a sustainable society and improving our quality of life.

Role of sleep for encoding of emotional memory

Total sleep deprivation (TSD) has been consistently found to impair encoding of information during ensuing wakefulness, probably through suppressing NonREM (non-rapid eye movement) sleep. However, a possible contribution of missing REM sleep to this encoding impairment after TSD has so far not been systematically examined in humans, although such contribution might be suspected in particular for emotional information. Here, in two separate experiments in young healthy men, we compared effects of TSD and of selective REM sleep deprivation (REMD), relative to respective control conditions of undisturbed sleep, on the subsequent encoding of neutral and emotional pictures. The pictures were presented in conjunction with colored frames to also assess related source memory. REMD was achieved by tones presented contingently upon initial signs of REM sleep. Encoding capabilities were examined in the evening (18:00h) after the experimental nights, by a picture recognition test right after encoding. TSD significantly decreased both the rate of correctly recognized pictures and of recalled frames associated with the pictures. The TSD effect was robust and translated into an impaired long term memory formation, as it was likewise observed on a second recognition testing one week after the encoding phase. Contrary to our expectation, REMD did not affect encoding in general, or particularly of emotional pictures. Also, REMD did not affect valence ratings of the encoded pictures. However, like TSD, REMD distinctly impaired vigilance at the time of encoding. Altogether, these findings indicate an importance of NonREM rather than REM sleep for the encoding of information that is independent of the emotionality of the materials.

Spillover effect of congestion charging on pro-environmental behavior

Abstract This paper reports an examination of a spillover effect from a real-world intervention policy of traffic congestion charging that impacted various pro-environmental behaviors. A mailed questionnaire surveyed randomly sampled car owners living in Stockholm County (Sweden) to gather data on travel modes and pro-environmental behavior before and after the introduction of a trial congestion charging policy in Stockholm. Results of paired t test on 291 valid samples revealed that this policy not only directly mitigates traffic congestion (i.e., a direct effect of the policy intervention), but it also indirectly ‘spills over’ to affect pro-environmental behaviors in nontransportation situations (resource and energy use). A spillover to pro-environmental behavior was confirmed by respondents who shifted their travel mode from car to pro-environmental travel mode. Interestingly, the spillover was also confirmed in a group of respondents who remained in the pro-environmental travel mode and others who adversely shifted away from a pro-environmental travel mode to cars. Results suggest that the spillover effect from an environmental policy intervention can have considerable impact on facilitating pro-environmental behaviors and surrounding issues in more general contexts, thus warranting careful evaluation with a wider perspective.

Can a short nap and bright light function as implicit learning and visual search enhancers

The present study examined effects of a short nap (20 min) and/or bright light (2000 lux) on visual search and implicit learning in a contextual cueing task. Fifteen participants performed a contextual cueing task twice a day (1200–1330 h and 1430–1600 h) and scored subjective sleepiness before and after a short afternoon nap or a break period. Participants served a total of four experimental conditions (control, short nap, bright light and short nap with bright light). During the second task, bright light treatment (BLT) was applied in the two of the four conditions. Participants performed both tasks in a dimly lit environment except during the light treatment. Results showed that a short nap reduced subjective sleepiness and improved visual search time, but it did not affect implicit learning. Bright light reduced subjective sleepiness. A short nap in the afternoon could be a countermeasure against sleepiness and an enhancer for visual search. Practitioner Summary: The study examined effects of a short afternoon nap (20 min) and/or bright light (2000 lux) on visual search and implicit learning. A short nap is a powerful countermeasure against sleepiness compared to bright light exposure in the afternoon.

Total sleep deprivation decreases flow experience and mood status

Background The purpose of this study was to examine the effect of sleep deprivation on flow experience. Methods Sixteen healthy male volunteers of mean age 21.4±1.59 (21–24) years participated in two experimental conditions, ie, sleep-deprivation and normal sleep. In the sleep-deprived condition, participants stayed awake at home for 36 hours (from 8 am until 10 pm the next day) beginning on the day prior to an experimental day. In both conditions, participants carried out a simple reaction time (psychomotor vigilance) task and responded to a questionnaire measuring flow experience and mood status. Results Flow experience was reduced after one night of total sleep deprivation. Sleep loss also decreased positive mood, increased negative mood, and decreased psychomotor performance. Conclusion Sleep deprivation has a strong impact on mental and behavioral states associated with the maintenance of flow, namely subjective well-being.