Sophie Blanchet

Enhancement of episodic memory in young and healthy adults: a paired-pulse TMS study on encoding and retrieval performance.

Transcranial magnetic stimulation (TMS) is a neurophysiological tool that can transiently influence brain excitability and improve cognitive performance. Facilitation effects induced by low frequency repetitive TMS on memory functions have been shown in a few studies in young and healthy participants [29] and in older individuals with memory complaints [40]. However, regions specifically involved in encoding and retrieval were not always systematically targeted. We thus aimed to facilitate episodic memory with online TMS systematically applied over the left or right dorsolateral prefrontal cortex (DLPFC) while participants were performing a recognition task. We applied online paired-pulse TMS (ppTMS) (15 ms inter-stimulus interval) either during encoding or retrieving of verbal or non-verbal material. Participants were 11 right-handed young individuals (21.33 ± 2.27 years old). Repeated measures ANOVA showed shorter reaction time when ppTMS are applied over the left DLPFC during encoding as compared to right homologous stimulation or to Sham condition. In contrast, ppTMS over the right DLPFC during retrieval was associated with shorter reaction times compared to left homologous stimulation. Overall, our data support for the first time that online ppTMS over the DLPFCs is capable of hastening memory processes in young and healthy individuals.

Paired-pulse transcranial magnetic stimulation over the dorsolateral prefrontal cortex interferes with episodic encoding and retrieval for both verbal and non-verbal materials

Neuroimaging studies report that encoding and retrieval processes of episodic memory constantly activate the left and right prefrontal cortex, even in the simplest memory tasks. Conversely, individuals with frontal lesions displayed impaired memory performance mainly in the most complex memory tasks. This discrepancy regarding the involvement of dorsolateral prefrontal cortex (DLPFC) may be explained by methodological divergences. Our goal was to study the critical role of the DLPFC in episodic encoding and retrieval processes according to the nature of the material (verbal or non-verbal) by using transcranial magnetic stimulation (TMS). Eighteen healthy adults performed a recognition task with words or random shapes. Paired-pulse TMS was applied (3-ms inter-pulse interval, at 90% of motor threshold) for inducing transient and safe interferences over the left or right DLPFCs during encoding or retrieval. Data analysis showed a reduced discrimination rate following TMS over the left DLPFC during encoding, as compared to a sham condition. Both hit and discrimination rates were also reduced after TMS over the right DLPFC, compared to TMS over left DLPFC, during retrieval. There was no difference between verbal and non-verbal material. Our results showed that the left and the right DLPFC play a critical role respectively in episodic encoding and retrieval processes for both verbal and non-verbal materials. Our findings are discussed in light of the findings obtained from other complementary approaches.

Event-related potential study of dynamic neural mechanisms of semantic organizational strategies in verbal learning

Neuroimaging and neuropsychological data indicate that the frontal regions are implicated in semantic organizational strategies in verbal learning. Whereas these approaches tend to adopt a localizationist view, we used event-related potentials (ERPs) to investigate the dynamic neural mechanisms involved in these strategies. We recorded ERPs using a 128-channel system in 12 young adults (23.75+/-3.02 years) during 3 encoding conditions that manipulated the levels of semantic organization demands. In the Unrelated condition, the words to encode did not share any semantic attributes. For both Spontaneous and Guided conditions, the words in each list were drawn from four semantic categories. In the Spontaneous condition, participants were not informed about the semantic relationship between items. In contrast, in the Guided condition, participants were instructed to improve their subsequent recall by mentally regrouping related items with the aid of category labels. Results indicated that the P200 amplitude increased with the greater organizational demand of semantic strategies. In contrast, the late positive component (LPC) amplitude was larger in both encoding conditions with semantic related words regardless of their instructions as compared to the Unrelated condition. Finally, there was greater right frontal sustained activity in the Spontaneous condition than in the Unrelated condition. Thus, our data indicate that the P200 is sensitive to attentional processes that increase with the organizational semantic demand. The LPC indexes associative processes voluntarily involved in linking related items together. Finally, the right frontal region appears to play an important role in the self-initiation of semantic organizational strategies.

Episodic Encoding in Normal Aging: Attentional Resources Hypothesis Extended to Musical Material

ABSTRACT The goal of the present study was to examine age-related changes in musical episodic memory for novel tunes. This was conducted by manipulating the encoding condition in a recognition paradigm. After receiving memory instructions (intentional condition), older and younger participants obtained equivalent hits. In contrast, when intentional encoding was accompanied by a dancing judgment (dancing + intentional condition), the recognition performance of the older persons was severely impaired. Impaired recognition was also found when participants only judged the excerpts without being instructed to memorize them (dancing judgment condition). Although older participants demonstrated a preserved ability to perform the dancing judgment on its own, this ability was not optimal and likely precluded the initiation of more elaborate encoding strategies. These results suggest that asking older persons to divide their attention in the study phase reduces the quality of their musical encoding. Given this extension to musical material, we discuss the notion that the age-related attentional resource decline appears to be domain-general rather than specific to verbal material.

Impact of divided attention during verbal learning in young adults following mild traumatic brain injury.

Primary objective: The goal of the present study was to assess the impact of mild traumatic brain injury (MTBI) on episodic memory performance in relation to attentional and executive control processes in young adults. Research design/methods: A verbal memory paradigm manipulating attentional load (full attention or divided attention) and semantic congruency between pairs of category-target words during encoding was administrated to 13 individuals with MTBI and 12 normal control participants. Environmental supports during retrieval (free recall, cued recall and recognition modes) were also manipulated. Main outcomes and results: Results show that recall performances of individuals with MTBI were similar to those of controls when words were encoded under full attention. In contrast, individuals with MTBI performed worse than control participants when encoding under divided attention, whatever the semantic link between pairs of words. Conclusions: By using a sensitive test, one was able to objectively measure subtle impairments in memory performance, suggesting a diminished availability of attentional resources after MTBI. Young adults’ learning of verbal material under divided attention might be compromised by the reduction of cognitive resources following MTBI. These findings are also discussed in light of different factors that can influence cognitive performance.

The division of visual attention affects the transition point from level walking to stair descent in healthy, active older adults

BACKGROUND Stair descent is a frequent daily activity that poses great risks for injury due to falling. Very little is understood about the attentional demands of stair descent and their changes with aging. The present study compared combined locomotor and cognitive functioning during different phases of stair descent between healthy young and older individuals. METHODS Sixteen young and sixteen healthy older subjects walked down a 5-step staircase, performing a simultaneous visual Stroop task (i.e., a dual task) during the approach, transition or steady-state descent phases in some trials. Three dimensional kinematics of trunk and foot motion were recorded along with the accuracy and dual task costs (DTCs) for responses to the Stroop stimuli. RESULTS Dual tasking influenced both gait and cognitive performance for all subjects, and older adults generally walked slower with higher foot clearances and had greater DTCs. Specific age differences were found at stair transition where older adults showed more attentional effects. CONCLUSIONS Healthy, active older adults showed changes to attention and planning due to normal aging specifically associated with a crucial point of fall risk during stair descent.

Executive dysfunction following a mild traumatic brain injury revealed in early adolescence with locomotor-cognitive dual-tasks

Abstract Objective: To compare gait parameters between children in early adolescence (EA) with and without a mild traumatic brain injury (mTBI) during dual-task walking (DTW). Methods: Children in EA with mTBI (n = 14; six girls) were compared to those without (n = 13; five girls) while walking in different combinations of obstacle avoidance and cognitive dual-tasks. Gait speed and fluidity and their related dual-task costs (DTC) were analysed along with foot clearance and proximity to the obstacle. Results: No group effects were found for gait speed, proximity or clearance, but were found for fluidity DTC, specifically during the dual Stroop task and when crossing the deeper obstacle. There were also group differences for fluidity during the planning of obstacle avoidance for the narrow obstacle combined with the verbal fluency task and the deep obstacle with no cognitive task. Finally, gait fluidity showed group differences across unobstructed dual-task situations. Conclusions: Gait fluidity may be a more sensitive variable than gait speed for revealing executive dysfunction following mTBI in EA. Assessing DTW in level walking also seems to show a potential to reveal executive dysfunctions in this age group. These results provide direction for future research on clinical assessment using DTW post-mTBI in adolescents.

Maximal cardiorespiratory fitness testing in individuals with chronic stroke with cognitive impairment: practice test effects and test-retest reliability.

OBJECTIVES To evaluate, for individuals with chronic stroke with cognitive impairment, (1) the effects of a practice test on peak cardiorespiratory fitness test results; (2) cardiorespiratory fitness test-retest reliability; and (3) the relationship between individual practice test effects and cognitive impairment. DESIGN Cross-sectional. SETTING Rehabilitation center. PARTICIPANTS A convenience sample of 21 persons (men [n=12] and women [n=9]; age range, 48-81y; 44.9±36.2mo poststroke) with cognitive impairments who had sufficient lower limb function to perform the test. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURE Peak oxygen consumption (Vo(2)peak, ml·kg(-1)·min(-1)). RESULTS Test-retest reliability of Vo(2)peak was excellent (intraclass correlation coefficient model 2,1 [ICC2,1]=.94; 95% confidence interval [CI], .86-.98). A paired t test showed that there was no significant difference for the group for Vo(2)peak obtained from 2 symptom-limited cardiorespiratory fitness tests performed 1 week apart on a semirecumbent cycle ergometer (test 2-test 1 difference, -.32ml·kg(-1)·min(-1); 95% CI, -.69 to 1.33ml·kg(-1)·min(-1); P=.512). Individual test-retest differences in Vo(2)peak were, however, positively related to general cognitive function as measured by the Mini-Mental State Examination (ρ=.485; P<.026). CONCLUSIONS Vo(2)peak can be reliably measured in this group without a practice test. General cognitive function, however, may influence the effect of a practice test in that those with lower general cognitive function appear to respond differently to a practice test than those with higher cognitive function.

Normative data for the Dementia Rating Scale-2 in the French-Quebec population.

The Dementia Rating Scale-2 is used to measure cognitive status of adults with cognitive impairment, especially of the degenerative type, by assessing five cognitive functions, namely attention, initiation/perseveration, construction, conceptualization, and memory. The present study aimed to establish normative data for this test in the elderly French-Quebec population. A total of 432 French-speaking elders from the province of Quebec (Canada), aged 50 to 85 years, were administered the Dementia Rating Scale-2. Age and education were found to be associated with the total score on the test, while gender was not. Percentile ranks were then calculated for age- and education-stratified groups. Previous studies have shown that cultural background can affect performance on the DRS and the development of culture-specific norms for French-speaking Quebecers could be very useful to clinicians and researchers working with this population.

Item-related versus task-related activity during encoding and retrieval in verbal and non-verbal episodic memory: an event-related potential study.

In the past 10 years, functional neuroimaging studies have elucidated the role of the prefrontal cortex in memory encoding and retrieval. However, it is still unclear whether these activations reflect item- or task-related activities. In the present study, Event-Related Potentials (ERPs) were used to distinguish item-related activity from task-related activity in both encoding and retrieval processes. This activity was assessed with both verbal and non-verbal material. A recognition paradigm with words or random shapes was administered to 12 young participants. Memory elicited ERPs were compared to those evoked by control tasks that used similar material. The distribution of the N400 was found to be larger on left frontal than right frontal areas for verbal material, however, this was the case in the control and memory conditions as well. This finding likely reflects the sensitivity of this component to processing verbal material. The LPC amplitude was greater in the non-verbal encoding than the non-verbal control condition, whereas in retrieval it was larger than the control condition for both verbal and non-verbal material. Thus, item-related activity is determined by an interaction between properties of the material and the task instructions. Task-related activity was found for non-verbal material: compared to the control condition, the memory condition of non-verbal material elicited bilateral and right frontal activity in encoding and retrieval processes. No task-related effect was reported with the verbal material. Material differences in eliciting task-related effects are discussed in terms of their relation to elaborative and effortful processes.