Neural correlates of active controlled retrieval development: An exploratory ERP study.

Working memory is composed of different processes and encompasses not only the temporary storage of information but also its manipulation in order to perform complex cognitive activities. During childhood, one of these manipulation processes, namely active controlled retrieval, improves significantly between the age of 6 to 10, suggesting that the neuronal network supporting this function undergoes substantial maturational changes. The present study examined the neural activity of 14 healthy children and 14 adults while performing an active controlled retrieval task. Results showed differences in brain activity according to active controlled retrieval in a 300-500 ms window corresponding to the retrieval period. Active controlled retrieval was associated with a P3b-like potential in parietal sites for both children and adults. In fronto-central sites, children demonstrated a "N400 like" potential associated with active retrieval processing. These results are discussed in terms of maturational development.

The Impact of a Motor-Cognitive Remediation Program on Attentional Functions of Preschoolers With ADHD Symptoms.

OBJECTIVE: The purpose of this study was to measure the impact of the motor-cognitive remediation program (MCRP) that uses sensorimotor and visual-motor imagery techniques on attentional functions in preschoolers with ADHD symptoms. METHOD: A total of 15 high-risk preschoolers were selected based on high ADHD symptoms. An experimental group participated in the MCRP and was compared with a control group. The MCRP consisted of 30 activities, 3 times a week, during 12 weeks. RESULTS: Children in the experimental group improved significantly for orienting (selective attention) and executive control (inhibition, stopping, and engaging mental operations) compared with the control group. CONCLUSION: These results are a first step to support the postulate that training specific attentional functions by sensorimotor activities and visual-motor imagery has an impact on the cognitive network of attention. This study suggests the potential value of MCRP addressed to preschoolers with ADHD symptoms.

Differences between patterns of brain activity associated with semantics and those linked with phonological processing diminish with age.

It is widely believed that language function tends to show little age-related performance decline. Indeed, some older individuals seem to use compensatory mechanisms to maintain a high level of performance when submitted to lexical tasks. However, how these mechanisms affect cortical and subcortical activity during semantic and phonological processing has not been extensively explored. The purpose of this study was to look at the effect of healthy aging on cortico-subcortical routes related to semantic and phonological processing using a lexical analogue of the Wisconsin Cart-Sorting Task. Our results indicate that while young adults tend to show increased activity in the ventrolateral prefrontal cortex, the dorsolateral prefrontal cortex, the fusiform gyrus, the ventral temporal lobe and the caudate nucleus during semantic decisions and in the posterior Broca's area (area 44), the temporal lobe (area 37), the temporoparietal junction (area 40) and the motor cortical regions during phonological decisions, older individuals showed increased activity in the dorsolateral prefrontal cortex and motor cortical regions during both semantic and phonological decisions. Furthermore, when semantic and phonological decisions were contrasted with each other, younger individuals showed significant brain activity differences in several regions while older individuals did not. Therefore, in older individuals, the semantic and phonological routes seem to merge into a single pathway. These findings represent most probably neural reserve/compensation mechanisms, characterized by a decrease in specificity, on which the elderly rely to maintain an adequate level of performance.

Changes in regional and temporal patterns of activity associated with aging during the performance of a lexical set-shifting task.

Some older individuals seem to use compensatory mechanisms to maintain high-level performance when submitted to cognitive tasks. However, whether and how these mechanisms affect fronto-striatal activity has never been explored. The purpose of this study was to investigate how aging affects brain patterns during the performance of a lexical analog of the Wisconsin Card Sorting Task, which has been shown to strongly depend on fronto-striatal activity. In the present study, both younger and older individuals revealed significant fronto-striatal loop activity associated with planning and execution of set-shifts, though age-related striatal activity reduction was observed. Most importantly, while the younger group showed the involvement of a "cognitive loop" during the receiving negative feedback period (which indicates that a set-shift will be required to perform the following trial) and the involvement of a "motor loop" during the matching after negative feedback period (when the set-shift must be performed), older participants showed significant activation of both loops during the matching after negative feedback period only. These findings are in agreement with the "load-shift" model postulated by Velanova et al. (Velanova K, Lustig C, Jacoby LL, Buckner RL. 2007. Evidence for frontally mediated controlled processing differences in older adults. Cereb Cortex. 17:1033-1046.) and indicate that the model is not limited to memory retrieval but also applies to executive processes relying on fronto-striatal regions.

Investigating the long-lasting residual effect of a set shift on frontostriatal activity.

Previous studies have shown the involvement of the ventrolateral prefrontal cortex (PFC) and the caudate nucleus when performing a set shift. However, the effect of set shifting on the frontostriatal activity observed during the later trials within a series of same-set classifications has yet to be determined. Here, young healthy adults underwent the functional magnetic resonance imaging while performing a card-sorting task in which the classification rule was provided prior to each trial. We observed a significant activation in the dorsolateral PFC, regardless of whether a set shift occurred or not. By contrast, the ventrolateral PFC and caudate nucleus showed an increased activity in both the shifting trials versus the control and in trials where the same rule was applied for a few trials before a set shift occurred, unlike trials where the same rule was applied for a longer period. Finally, decreased activity in the caudate nucleus correlated with an increasing trial position in trials where no set shift occurred, suggesting that the more a rule is executed, the better it is established. We argue that a new rule needs to be performed multiple times until the brain areas usually associated with the set shifting are no longer significantly required anymore.

Fronto-striatal contribution to lexical set-shifting.

Fronto-striatal circuits in set-shifting have been examined in neuroimaging studies using the Wisconsin Card Sorting Task (WCST) that requires changing the classification rule for cards containing visual stimuli that differ in color, shape, and number. The present study examined whether this fronto-striatal contribution to the planning and execution of set-shifts is similar in a modified sorting task in which lexical rules are applied to word stimuli. Young healthy adults were scanned with functional magnetic resonance imaging while performing the newly developed lexical version of the WCST: the Wisconsin Word Sorting Task. Significant activation was found in a cortico-striatal loop that includes area 47/12 of the ventrolateral prefrontal cortex (PFC), and the caudate nucleus during the planning of a set-shift, and in another that includes the posterior PFC and the putamen during the execution of a set-shift. However, in the present lexical task, additional activation peaks were observed in area 45 of the ventrolateral PFC area during both matching periods. These results provide evidence that the functional contributions of the various fronto-striatal loops are not dependent on the modality of the information to be manipulated but rather on the specific executive processes required.

Basal ganglia and frontal involvement in self-generated and externally-triggered finger movements in the dominant and non-dominant hand.

Although there are a number of functional neuroimaging studies that have investigated self-initiated and externally-triggered movements, data directly comparing right and left hands in this context are very scarce. The goal of this study was to further understand the role of the basal ganglia and prefrontal cortex in the realm of self-initiated and externally-triggered right and left hand movements. Young healthy right-handed adults performed random, follow and repeat conditions of a finger moving task with their right and left hands, while being scanned with functional magnetic resonance imaging. Significant activation of the dorsolateral prefrontal cortex was observed when comparing the self-initiated movements with the repeated control and externally-triggered movements when using either hand in agreement with its role in monitoring. The caudate nucleus activation was found during self-initiated conditions compared with the control condition when either hand was used, showing that it is particularly involved when a new movement needs to be planned. Significant putamen activation was observed in all within-hand contrasts except for the externally-triggered vs. control condition when using the left hand. Furthermore, greater putaminal activation was found for the left vs. the right hand during the control condition, but for the right vs. the left hand subtraction for the self-initiated condition. Our results show that the putamen is particularly involved in the execution of non-routine movements, especially if those are self-initiated. Furthermore, we propose that, for right-handed people performing fine movements, as far as putamen involvement is concerned, the lack of proficiency of the non-dominant hand may prevail over other task demands.