Spatial and contextual memories

Sleep modulates the neural substrates of both spatial and contextual memory consolidation.
Geraldine Rauchs, Pierre Orban, Christina Schmidt, Genevieve Albouy, Evelyne Balteau, Christian Degueldre, Caroline Schnackers, Virginie Sterpenich, Gilberte Tinguely, Andre Luxen, Pierre Maquet, Philippe Peigneux
PLoS ONE 2008;3(8):e2949.

Background: It is known that sleep reshapes the neural representations that subtend the memories acquired while navigating in a virtual environment. However, navigation is not process-pure, as manifold learning components contribute to performance, notably the spatial and contextual memory constituents. In this context, it remains unclear whether post-training sleep globally promotes consolidation of all of the memory components embedded in virtual navigation, or rather favors the development of specific representations.

Methods: Here, we investigated the effect of post-training sleep on the neural substrates of the consolidation of spatial and contextual memories acquired while navigating in a complex 3D, naturalistic virtual town. Using fMRI, we mapped regional cerebral activity during various tasks designed to tap either the spatial or the contextual memory component, or both, 72 h after encoding with or without sleep deprivation during the first post-training night.

Results: Behavioral performance was not dependent upon post-training sleep deprivation, neither in a natural setting that engages both spatial and contextual memory processes nor when looking more specifically at each of these memory
representations. At the neuronal level however, analyses that focused on contextual memory revealed distinct correlations between performance and neuronal activity in frontal areas associated with recollection processes after post-training sleep,
and in the parahippocampal gyrus associated with familiarity processes in sleep-deprived participants. Likewise, efficient spatial memory was associated with posterior cortical activity after sleep whereas it correlated with parahippocampal/
medial temporal activity after sleep deprivation. Finally, variations in place-finding efficiency in a natural setting encompassing spatial and contextual elements were associated with caudate activity after post-training sleep, suggesting
the automation of navigation.

Conclusion: These data indicate that post-training sleep modulates the neural substrates of the consolidation of both the spatial and contextual memories acquired during virtual navigation.

Emotional Context

Decoding of affective facial expressions in the context of emotional situations
Monika Sommera, Katrin Döhnela, Jörg Meinhardtb and Göran Hajaka
Neuropsychologia Volume 46, Issue 11, September 2008, Pages 2615-2621

Background: The ability to recognize other persons’ affective states and to link these with aspects of the current situation arises early in development and is precursor functions of a Theory of Mind (ToM). Until now, studies investigated either the processing of affective faces or affective pictures.

Methods: In the present study, we tried to realize a scenario more similar to every day situations. We employed fMRI and used a picture matching task to explore the neural correlates associated with the integration and decoding of facial affective expressions in the context of affective situations. In the emotion condition, the participants judged an emotional facial expression with respect to the content of an emotional picture. In the two other conditions, participants indicated colour matches on the background of either affective or scrambled pictures.

Results: In contrast to colour matching on scrambled pictures, colour matching on emotional pictures resulted in longer reaction times and increased activation of the bilateral fusiform and occipital gyrus. These results indicated that, although task irrelevant, participants may attend to the emotional background of the pictures. The emotion task was associated with higher reaction times and with activation of the bilateral fusiform and occipital gyrus. Additionally, emotion attribution induced left amygdala activity. Possibly, attention processes and amygdala projections modulated the activation found in the occipital and fusiform areas. Furthermore, the involvement of the amygdala in the ToM precursor ability to link facial expressions with an emotional situation may indicate that the amygdala is involved in the development of stable ToM abilities.

Age-Related Insomnia

Age-Related Reduction in the Maximal Capacity for Sleep—Implications for Insomnia
Elizabeth B. Klerman and Derk-Jan Dijk
Current Biology 18, 1–6, August 5, 2008

Background: Sleep changes markedly across the life span and complaints about insomnia are prevalent in older people. Whether age-related alterations in sleep are due to modifications in social factors, circadian physiology, homeostatic drive, or
the ability to sleep remains unresolved.

Methods: We assessed habitual sleep duration at home and then quantified daytime sleep propensity, sleep duration, and sleep structure in an inpatient protocol that included extended sleep opportunities covering 2/3 of the circadian cycle (12 hr at night and 4 hr in the afternoon) for 3–7 days in 18 older and 35 younger healthy men and women.

Results: At baseline, older subjects had less daytime sleep propensity than did younger subjects. Total daily sleep duration, which was initially longer than habitual sleep duration, declined during the experiment to asymptotic values that were 1.5 hr shorter in older (7.4 6 0.4 SEM, hour) than in younger subjects (8.9 6 0.4). Rapid eye-movement sleep and non-rapid-eye-movement sleep contributed about equally to this reduction.

Conclusions: Thus, in the absence of social and circadian constraints, both daytime sleep propensity and the maximal capacity for sleep are reduced in older people. These data have important implications for understanding age-related insomnia.

How Sleep affects Memory and Congition

Functional neuroimaging insights into how sleep and sleep deprivation affect memory and cognition.
Chee Michael WL and Chuah Lisa YM b
Current Opinion in Neurology. 24(4):417-423, August 2008.

Purpose of review: The review summarizes current knowledge about what fMRI has revealed regarding the neurobehavioral correlates of sleep deprivation and sleep-dependent memory consolidation.

Recent findings: Functional imaging studies of sleep deprivation have characterized its effects on a number of cognitive domains, the best studied of these being working memory. There is a growing appreciation that it is important to consider inter individual differences in vulnerability to sleep deprivation, task and task difficulty when interpreting imaging results. Our understanding of the role of sleep and the dynamic evolution of offline memory consolidation has benefited greatly from human imaging studies. Both hippocampal-dependent and hippocampal-independent memory systems have been studied.

Summary: Functional imaging studies contrasting sleep-deprived and well-rested brains provide substantial evidence that sleep is highly important for optimal cognitive function and learning. The experimental paradigms developed to date merit evaluation in clinical settings to determine the impact of sleep disruption in sleep disorders.

Computer that works like the brain?

Researcher Kwabena Boahen is looking for ways to mimic the brain's supercomputing powers in silicon -- because the messy, redundant processes inside our heads actually make for a small, light, superfast computer.

Emotion Modulates Default Activity

Emotional Experience Modulates Brain Activity During Fixation Periods Between Tasks
Sean Pitroda, Mike Angstadt, Michael S. McCloskey, Emil F. Coccaro, K. Luan Phan
Neuroscience Letters

Background: Functional imaging studies have begun to identify a set of brain regions whose brain activity is greater during 'rest' (e.g., fixation) states than during cognitive tasks. It has been posited that these regions constitute a network that supports the brain's default mode, which is temporarily suspended during specific goal-directed behaviors. Exogenous tasks that require cognitive effort are thought to command reallocation of resources away from the brain's default state. However, it remains unknown if brain activity during fixation periods between active task periods is influenced by previous task-related emotional content.

Methods: We examined brain activity during periods of FIXATION (viewing and rating gray-scale images) interspersed among periods of viewing and rating complex images ('PICTURE') with positive, negative, and neutral affective content.

Results: We show that a selected group of brain regions (PCC, precuneus, IPL, vACC) do exhibit activity that is greater during FIXATION (>PICTURE); these regions have previously been implicated in the "default brain network". In addition, we report that activity within precuneus and IPL in the FIXATION period is attenuated by the precedent processing of images with positive and negative emotional content, relative to non-emotional content.

Conclusion: These data suggest that the activity within regions implicated in the default network is modulated by the presence of environmental stimuli with motivational salience and, thus, adds to our understanding of the brain function during periods of low cognitive, emotional, or sensory demand.

Persistence of Emotional Memories Over Time

Role of Amygdala Connectivity in the Persistence of Emotional Memories Over Time: An Event-Related fMRI Investigation
Maureen Ritchey, Florin Dolcos and Roberto Cabeza
Cerebral Cortex, 2008

Background: According to the consolidation hypothesis, enhanced memory for emotional information reflects the modulatory effect of the amygdala on the medial temporal lobe (MTL) memory system during consolidation. Although there is evidence that amygdala--MTL connectivity enhances memory for emotional stimuli, it remains unclear whether this enhancement increases over time, as consolidation processes

Methods: They used functional magnetic resonance imaging to measure encoding activity predicting memory for emotionally negative and neutral pictures after short (20-min) versus long (1-week) delays.

Results: Memory measures distinguished between vivid remembering (recollection) and feelings of knowing (familiarity). Consistent with the consolidation hypothesis, the persistence of recollection over time (long divided by short) was greater for emotional than neutral pictures. Activity in the amygdala predicted subsequent memory to a greater extent for emotional than neutral pictures. Although this advantage did not vary with delay, the contribution of amygdala--MTL connectivity to subsequent memory for emotional items increased over time. Moreover, both this increase in connectivity and amygdala activity itself were correlated with individual differences in recollection persistence for emotional but not neutral pictures.

Conclusion: These results suggest that the amygdala and its connectivity with the MTL are critical to sustaining emotional memories over time, consistent with the consolidation hypothesis.

Small-world network organization during sleep

The functional connectivity of different EEG bands moves towards small-world network organization during sleep.
Ferri R, Rundo F, Bruni O, Terzano MG, Stam CJ.
Clin Neurophysiol. 2008 Sep;119(9):2026-36.

Background: To analyze the functional connectivity patterns of the different EEG
bands during wakefulness and sleep (different sleep stages and cyclic alternating
pattern (CAP) conditions), using concepts derived from Graph Theory.

Methods: They evaluated spatial patterns of EEG band synchronization between all possible pairs of electrodes (19) placed over the scalp of 10 sleeping healthy young normal subjects using two graph theoretical measures: the clustering coefficient (Cp) and the characteristic path length (Lp). The measures were obtained during wakefulness and the different sleep stages/CAP conditions from the real EEG connectivity networks and randomized control (surrogate) networks (Cp-s and Lp-s).

Results: They found the values of Cp and Lp compatible with a small-world network organization in all sleep stages and for all EEG bands. All bands below 15Hz showed an increase of these features during sleep (and during CAP-A phases in particular), compared to wakefulness.

Conclusion: The results of this study seem to confirm the initial hypothesis that during sleep there exists a clear trend for the functional connectivity of the EEG to move forward to an organization more similar to that of a small-world network, at least for the frequency bands lower than 15Hz. Sleep network "reconfiguration" might be one of the key mechanisms for the understanding of the "global" and "local" neural plasticity taking place during sleep.

Positive Psychology

Martin Seligman talks about psychology -- as a field of study and as it works one-on-one with each patient and each practitioner. As it moves beyond a focus on disease, what can modern psychology help us to become?

Authorship Plagiarism

Plagiarism is the unauthorized use or close imitation of the language and thoughts of another author and the representation of them as one's own original work. (Wiki)

Now let's think of that definition in the context of authorship in science.

According to the study by Swazey, Anderson and Lewis the rates of plagiarism and inappropriate authorship were reported to be similar by both faculty and students. They found that inappropriate authorship was slightly more frequent than plagiarism with one the twist: While plagiarism was about three times more likely to be committed by students than by faculty, inappropriate authorship was about three times more likely to be committed by faculty than by students.

I think the National Academy of Sciences in the study of scientific misconduct should include the most frequent and important issue of possible misconduct relevant to the designation of authorship besides aspects like fabrication, falsification, and plagiarism.