The Role of Sleep in the Selective Reconsolidation of Declarative Memories

While sleep has been shown to be involved in memory consolidation and the selective enhancement of newly acquired memories of future relevance (Wilhelm, et al., 2011), limited research has investigated the role of sleep or future relevance in processes of memory reconsolidation. The current research employed a list-method directed forgetting procedure in which participants learned two lists of syllable pairs on Night 1 and received directed forgetting instructions on Night 2. On Night 2, one group (Labile; n = 15) received a memory reactivation treatment consisting of reminders designed to return memories of the learned lists to a labile state. A second group (Stable, n = 16) received similar reminders designed to leave memories of the learned lists in their stable state. No differences in forgetting were found across the two lists or groups. However, a negative correlation between frontal delta (1 – 4 Hz) electroencephalographic (EEG) power during Early Stage 2 non-rapid eye movement (NREM) sleep and forgetting of to-beremembered material was found exclusively in the Labile group (r = -.61, p < .05). Further, central theta (4 – 8 Hz ) EEG power during rapid eye movement (REM) sleep was found to correlate with directed forgetting exclusively in the Labile group (r = .81, p < .001) and total forgetting in the Stable group (r = .50, p < .05). These observed relationships support the proposed hypothesis suggesting that sleep processes are involved in the reconsolidation of labile memories, and that this reconsolidation may be selective for memories of future relevance. A role for sleep in the beneficial reprocessing of memories through the selective reconsolidation of labile memories in NREM sleep and the weakening of memories in REM sleep is discussed.

Social competence following mild head injury and moderate traumatic brain injury: Investigating the neuropsychological relationships between arousal, social decision-making and depression

Client-directed long-term rehabilitative goals and life satisfaction following head injury emphasize the importance of social inclusion, rather than cognitive or physical, outcomes. However, very little research has explored the socio-emotional factors that pose as barriers to social reintegration following injury. This study investigates social barriers following head injury (i.e., decision-making - Iowa Gambling Task [IGT] and mood – depression) and possible amelioration of those challenges (through treatment) in both highly functioning university students with and without mild head injury (MHI) and in individuals with moderate traumatic brain injury (TBI). An arousal manipulation using emotionally evocative stimuli was introduced to manipulate the subject’s physiological arousal state. Seventy-five university students (37.6% reporting a MHI) and 11 patients with documented moderate TBI were recruited to participate in this quasi-experimental study. Those with head injury were found to be physiologically underaroused (on measures of electrodermal activation [EDA] and pulse) and were less sensitive to the negative effects of punishment (i.e., losses) in the gambling task than those without head injury, with greater impairment being observed for the moderate TBI group. The arousal manipulation, while effective, was not able to maintain a higher state of arousal in the injury groups across trials (i.e., their arousal state returned to pre-manipulation levels more quickly than their non-injured cohort), and, subsequently, a performance improvement was not observed on the IGT. Lastly, head injury was found to contribute to the relationship between IGT performance and depressive symptom acknowledgment and mood status in persons with head injury. This study indicates the possible important role of physiological arousal on socio- emotional behaviours (decision-making, mood) in persons with even mild, non-complicated head injuries and across the injury severity continuum.