Physical Exercise Performed Four Hours after Learning Improves Memory Retention and Increases Hippocampal Pattern Similarity during Retrieval

Contains fulltext : 167385.pdf (Publisher’s version ) (Closed access)Persistent long-term memory depends on successful stabilization and integration of new memories after initial encoding [1, 2]. This consolidation process is thought to require neuromodulatory factors such as dopamine, noradrenaline, and brain-derived neurotrophic factor [3-7]. Without the release of such factors around the time of encoding, memories will decay rapidly [3, 5, 6, 8]. Recent studies have shown that physical exercise acutely stimulates the release of several consolidation-promoting factors in humans [9-14], raising the question of whether physical exercise can be used to improve memory retention [15-17]. Here, we used a single session of physical exercise after learning to exogenously boost memory consolidation and thus long-term memory. Three groups of randomly assigned participants first encoded a set of picture-location associations. Afterward, one group performed exercise immediately, one 4 hr later, and the third did not perform any exercise. Participants otherwise underwent exactly the same procedures to control for potential experimental confounds. Forty-eight hours later, participants returned for a cued-recall test in a magnetic resonance scanner. With this design, we could investigate the impact of acute exercise on memory consolidation and retrieval-related neural processing. We found that performing exercise 4 hr, but not immediately, after encoding improved the retention of picture-location associations compared to the no-exercise control group. Moreover, performing exercise after a delay was associated with increased hippocampal pattern similarity for correct responses during delayed retrieval. Our results suggest that appropriately timed physical exercise can improve long-term memory and highlight the potential of exercise as an intervention in educational and clinical settings

Decreased Left Caudate Volume Is Associated with Increased Severity of Autistic-Like Symptoms in a Cohort of ADHD Patients and Their Unaffected Siblings

Autism spectrum disorder (ASD) symptoms frequently occur in individuals with attention-deficit/ hyperactivity disorder (ADHD). While there is evidence that both ADHD and ASD have differential structural brain correlates, knowledge of the structural brain profile of individuals with ADHD with raised ASD symptoms is limited. The presence of ASD-like symptoms was measured by the Children's Social Behavior Questionnaire (CSBQ) in a sample of typically developing controls (n = 154), participants with ADHD (n = 239), and their unaffected siblings (n = 144) between the ages of 8 and 29. Structural magnetic resonance imaging (MRI) correlates of ASD ratings were analysed by studying the relationship between ASD ratings and grey matter volumes using mixed effects models which controlled for ADHD symptom count and total brain volume. ASD ratings were significantly elevated in participants with ADHD relative to controls and unaffected siblings. For the entire group (participants with ADHD, unaffected siblings and TD controls), mixed effect models revealed that the left caudate nucleus volume was negatively correlated with ASD ratings (t = 2.83; P = 0.005). The current findings are consistent with the role of the caudate nucleus in executive function, including the selection of goals based on the evaluation of action outcomes and the use of social reward to update reward representations. There is a specific volumetric profile associated with subclinical ASD-like symptoms in participants with ADHD, unaffected siblings and controls with the caudate nucleus and globus pallidus being of critical importance in predicting the level of ASD-like symptoms in all three groups.</p

The Role of Superior Temporal Cortex in Auditory Timing

Recently, there has been upsurge of interest in the neural mechanisms of time perception. A central question is whether the representation of time is distributed over brain regions as a function of stimulus modality, task and length of the duration used or whether it is centralized in a single specific and supramodal network. The answers seem to be converging on the former, and many areas not primarily considered as temporal processing areas remain to be investigated in the temporal domain. Here we asked whether the superior temporal gyrus, an auditory modality specific area, is involved in processing of auditory timing. Repetitive transcranial magnetic stimulation was applied over left and right superior temporal gyri while participants performed either a temporal or a frequency discrimination task of single tones. A significant decrease in performance accuracy was observed after stimulation of the right superior temporal gyrus, in addition to an increase in response uncertainty as measured by the Just Noticeable Difference. The results are specific to auditory temporal processing and performance on the frequency task was not affected. Our results further support the idea of distributed temporal processing and speak in favor of the existence of modality specific temporal regions in the human brain

Sleep supports selective retention of associative memories based on relevance for future utilization

Contains fulltext : 102880.pdf (publisher's version ) (Open Access)An outstanding question is whether memory consolidation occurs passively or involves active processes that selectively stabilize memories based on future utility. Here, we differentially modulated the expected future relevance of two sets of picture-location associations after learning. Participants first studied two sets of picture-location associations. After a baseline memory test, they were instructed that only one set of associations would be retested after a 14-hour delay. For half of the participants, this test-retest delay contained a night of sleep; for the other half the delay included a normal working day. At retest, participants were re-instructed and against their expectations tested on both sets of associations. Our results show that post-learning instruction about subsequent relevance selectively improves memory retention for specific associative memories. This effect was sleep-dependent; it was present only in the group of subjects for which the test-retest delay contained sleep. Moreover, time spent asleep for participants in this sleep group correlated with retention of relevant but not irrelevant associations; participants who slept longer forgot fewer associations from the relevant category. In contrast, participants that did not sleep forgot more relevant than irrelevant associations across the test-retest delay. In summary, our results indicate that it is possible to modulate the retention of selected memories after learning with simple verbal instructions on their future relevance. The finding that this effect depends on sleep demonstrates this state's active role in memory consolidation and may have utility for educational settings.6 p

Brain sites of stimulation.

<p>MNI coordinates on the single subject MNI template used to localize the right and left STG.</p

Results.

<p>A) Timeline of the experimental paradigm; B) Percentage of accurate responses and standard errors across the three TMS sites for the duration (white bars) and the frequency (black bars) discrimination tasks. Asterisk indicates significant differences in Tukey’s tests (* p<0.02). In order to check that the two tasks were well matched in terms of difficulty we also compared the two tasks after vertex stimulation (vertex Duration versus vertex Frequency: T₇ = −0.21 P = 0.8). C–E) Group accuracy data (number of hits/total number of targets) across different comparison durations, for rTMS of the vertex (□), right (○) and left (*) STG. The line fitting the symbols are averaged fitted functions (obtained fitting the group averaged data). Solid lines represent rTMS of the vertex, dashed lines rTMS of right STG and dotted lines rTMS of the left STG. C) is the duration discrimination task E) is the frequency discrimination task. D–F) JND (black bars) and PSE (white bars) group data for temporal (D) and frequency (F) discrimination tasks as a function of TMS conditions. Asterisk indicates significant differences in Tukey’s t-tests (* p = 0.04).</p

Context-dependent changes in functional connectivity of auditory cortices during the perception of object words

Contains fulltext : 102395.pdf (publisher's version ) (Open Access)Embodied theories hold that cognitive concepts are grounded in our sensorimotor systems. Specifically, a number of behavioral and neuroimaging studies have buttressed the idea that language concepts are represented in areas involved in perception and action [Pulvermueller, F. Brain mechanisms linking language and action. Nature Reviews Neuroscience, 6, 576-582, 2005; Barsalou, L. W. Perceptual symbol systems. Behavioral and Brain Sciences, 22, 577-660, 1999]. Proponents of a strong embodied account argue that activity in perception/action areas is triggered automatically upon encountering a word and reflect static semantic representations. In contrast to what would be expected if lexical semantic representations are automatically triggered upon encountering a word, a number of studies failed to find motor-related activity for words with a putative action-semantic component [Raposo, A., Moss, H. E., Stamatakis, E. A., & Tyler, L. K. Modulation of motor and premotor cortices by actions, action words and action sentences. Neuropsychologia, 47, 388-396, 2009; Rueschemeyer, S.-A., Brass, M., & Friederici, A. D. Comprehending prehending: Neural correlates of processing verbs with motor stems. Journal of Cognitive Neuroscience, 19, 855-865, 2007]. In a recent fMRI study, Van Dam and colleagues [Van Dam, W. O., Van Dijk, M., Bekkering, H., & Rueschemeyer, S.-A. Flexibility in embodied lexical-semantic representations. Human Brain Mapping, in press] showed that the degree to which a modality-specific region contributes to a representation considerably changes as a function of context. In the current study, we presented words for which both motor and visual properties (e.g., tennis ball, boxing glove) were important in constituting the concept. Our aim was to corroborate on earlier findings of flexible and context-dependent language representations by testing whether functional integration between auditory brain regions and perception/action areas is modulated by context. Functional connectivity was investigated by means of a psychophysiological interaction analysis, in which we found that bilateral superior temporal gyrus was more strongly connected with brain regions relevant for coding action information: (1) for Action Color words vs. Abstract words, and (2) for Action Color words presented in a context that emphasized action vs. a context that emphasized color properties.12 p

Mean performance for the WAKE and SLEEP group.

<p> <i>Performance is listed as the number of correct responses (maximum  = 60) with the Standard Error of the Mean in brackets.</i></p

Relevance modulated retention of picture-locations associations.

<p>A 3-way interaction was observed between SESSION, RELEVANCE and GROUP. Performance is shown here as the amount of forgetting between TEST and RETEST (the effect of SESSION, “memory loss”, Y-axis). Analysis showed that sleep decreased memory loss of relevant compared to irrelevant associations, whereas daytime wake showed an opposite effect. Error bars denote the standard error of the mean. Brackets indicate significant differences in post-hoc comparisons. * = p<0.05, ** = p<0.005.</p