Figure 1.
A- Finger Tapping Task, FTT. B- Experimental groups. Subjects were scanned during training and were divided in two groups according to the sleep condition on the first post-training night (SG: Sleep Group, SDG: Sleep Deprived Group). All the subjects were retested in the scanner three days later. C- Experimental design. Training and retest sessions consisted of 14 and 20 blocks respectively, each block consisting in 60 key presses. The untrained (U) sequence was proposed during retest, mixed with trained (T) sequence.
Figure 2.
Whiskers represent SEM. A- Left panel: Performance (mean block duration) improvement during training did not differ between the two groups. Middle panel: A significant ((*), p<0.05) offline gain in performance is observed in sleepers but not in sleep deprived subjects between the end of training (Tr) and the beginning of retest (Re). Right panel: Dynamics of mean time to perform a correct sequence (Mean, upper panel) and the standard deviation of difference between the data points (time to perform each correct sequence) and their power-law fit (Std, lower panel) computed over all subjects. Note that variability of performance follows a specific dynamics during training which does not parallel mean performance [2]. B- Left panel: Mean response time (RT) between two elements within a correct sequence for the first 10 correct sequences by block during both training and retest sessions. Note that the repetition effect is heterogeneous across blocks and that a significant fatigue effect manifests in block 8. Right panel: Between-session gains in performance are due to a rapid increase in RT during the retest session rather than to a slow-down in performance at the end of the training session ((*), p<0.05; (o), p>0.05).
Figure 3.
Functional imaging results for the training session.
Functional results are displayed at puncorrected<0.001 over the mean structural image of all subjects. In the insets, whiskers represent SEM. CN: Caudate Nucleus, HC: Hippocampus. A- Linear modulation of brain responses by performance consistency. Caudate nucleus responses increased during training in parallel to performance reproducibility. The dynamics of caudate activity follows a similar non-linear pattern as performance consistency during training. The functional connectivity between the caudate nucleus and frontal areas is proportional to performance variability during training [2]. B- Regression analysis between cerebral areas functionally connected with the caudate nucleus, in proportion to performance variability and gain in performance in the SG. Left panel: The strength of the functional connectivity (competitive interaction) between the caudate nucleus and hippocampo-cortical areas is correlated with the subsequent gains in performance on the learned sequence in the SG. Right panel: Regression plot of the strength of the functional connectivity (competitive interaction) between the caudate nucleus and the hippocampus related to performance variability against the gains in performance in the SG (block duration (s)) on the learned sequence. Each data point represents a single subject of the SG.
Table 1.
Functional results for the practice of the trained sequence during training and retest sessions.
Table 2.
Functional results for the training session.
Table 3.
Functional results for the main effect of session on the trained sequence (Retest – Training).
Figure 4.
Functional imaging results of the main effect of session on the learned sequence according to the sleep condition (Retest - Training).
Functional results are displayed at puncorrected<0.001 over the mean structural image of all subjects. Mean parameter estimates on the trained sequence during training and retest sessions (arbitrary units: a.u.) are presented in the insets where bars represent SEM. HC: Hippocampus, MPFC: Medial Prefrontal Cortex, VP: Ventral Putamen, PCC: Posterior Cingulate Cortex, ACC: Anterior Cingulate Cortex. A- Between-session effects in SG: In sleepers, responses increased in the HC and the MPFC at retest as compared to training. B- Between-session effects in SDG: In sleep-deprived subjects, responses increased from training to retest in the VP and in ACC and PCC.