Persistent implicit motor learning alterations following a mild traumatic brain injury sustained during late adulthood.

Introduction: The neurocognitive outcomes of sustaining a mild traumatic brain injury (mTBI) during late adulthood are vastly understudied. In young, asymptomatic adults, mTBI-related synaptic plasticity alterations have been associated with persistent implicit motor sequence learning impairments outlasting the usual cognitive recovery period. The current study examined whether uncomplicated mTBI sustained during late adulthood could exert persistent deleterious consequences on implicit motor sequence learning.Method: Thirty participants (aged 50-70 years) who experienced an uncomplicated mTBI within 3 to 24 months of testing, and 40 age-, sex- and education-equivalent healthy controls performed an implicit serial reaction time task (SRT task). The SRT task consisted of 10 blocks of a repeating sequence embedded among 4 random blocks. Participants also completed a battery of standardized neuropsychological tests of attention, memory and executive functioning.Results: While both mTBI participants and controls showed significant implicit motor sequence learning effects, the mTBI group achieved a lower level of competence at performing the SRT task as evidenced by smaller gains in reaction times across the 10 training blocks of the repeating sequence. The time elapsed since the injury was unrelated to implicit motor learning effects. There was no evidence of a persistent effect of mTBI on any neuropsychological domain compared to controls.Conclusions: Findings from this study suggest that a single mTBI sustained during older age may have persistent repercussions on training-dependent motor sequence learning capacity outlasting the recovery of mTBI symptoms and gold-standard neuropsychological tests performance.

Subtle long-term cognitive effects of a single mild traumatic brain injury and the impact of a three-month aerobic exercise intervention.

BACKGROUND: Although there is a growing body of literature on the impact of multiple concussions on cognitive function with aging, less is known about the long-term impact of sustaining a single mild traumatic brain injury (mTBI). Additionally, very few interventions exist to treat mTBI patients and prevent a possible accelerated cognitive decline. This study aimed to: 1) examine the long-term effects of a single mTBI on cognition in patients aged between 55 and 70 years old; and 2) evaluate the cognitive effects of an aerobic exercise program for these patients. METHODS: Thirty-five participants (average age: 58.89, SD=4.14) were assessed using neuropsychological tests. Among them, 18 hadsustained a mTBI two to seven years earlier. Significant differences in information processing speed, executive function and visual memory were found between controls and mTBI patients. Sixteen of the mTBI patients then engaged in a 12-week physical exercise program. They were divided into equivalent groups: 1) aerobic training (cycle ergometers); or 2) stretching exercises. The participants' cardiopulmonary fitness (VO2max) was evaluated pre- and postintervention and neuropsychological tests were re-administered postintervention. RESULTS: Participants from the aerobic group significantly improved their fitness compared to the stretching group. However, no between-group difference was found on neuropsychological measures postintervention. CONCLUSIONS: In summary, this study shows long-term cognitive effects of mTBI in late adulthood patients. Moreover, the controlled, 12-week aerobic exercise program did not lead to cognitive improvements in our small mTBI sample. Lastly, future directions in optimizing mTBI intervention are discussed.

Motor Learning Improvement Remains 3 Months After a Multisession Anodal tDCS Intervention in an Aging Population.

Healthy aging is associated with decline of motor function that can generate serious consequences on the quality of life and safety. Our studies aim to explore the 3-month effects of a 5-day multisession anodal transcranial direct current stimulation (a-tDCS) protocol applied over the primary motor cortex (M1) during motor sequence learning in elderly. The present sham-controlled aging study investigated whether tDCS-induced motor improvements previously observed 1 day after the intervention persist beyond 3 months. A total of 37 cognitively-intact aging participants performed five consecutive daily 20-min sessions of the serial-reaction time task (SRTT) concomitant with either anodal (n = 18) or sham (n = 19) tDCS over M1. All participants performed the Purdue Pegboard Test and transcranial magnetic stimulation (TMS) measures of cortical excitability were collected before, 1 day after and 3 months after the intervention. The last follow-up session also included the execution of the trained SRTT. The main findings are the demonstration of durable effects of a 5-day anodal tDCS intervention at the trained skill, while the active intervention did not differ from the sham intervention at both the untrained task and on measures of M1-disinhibition. Thus, the current article revealed for the first time the durability of functional effects of a-tDCS combined with motor training after only 5 days of intervention in an aging population. This finding provides evidence that the latter treatment alternative is effective in achieving our primary motor rehabilitation goal, that is to allow durable motor training effects in an aging population.

Multisession anodal transcranial direct current stimulation induces motor cortex plasticity enhancement and motor learning generalization in an aging population.

OBJECTIVES: The present aging study investigated the impact of a multisession anodal-tDCS protocol applied over the primary motor cortex (M1) during motor sequence learning on generalization of motor learning and plasticity-dependent measures of cortical excitability. METHODS: A total of 32 cognitively-intact aging participants performed five consecutive daily 20-min sessions of the serial-reaction time task (SRTT) concomitant with either anodal (n = 16) or sham (n = 16) tDCS over M1. Before and after the intervention, all participants performed the Purdue Pegboard Test (PPT) and Transcranial Magnetic Stimulation (TMS) measures of cortical excitability were collected. RESULTS: Relative to sham, participants assigned to the anodal-tDCS intervention revealed significantly greater performance gains on both the trained SRTT and the untrained PPT as well as a greater disinhibition of long-interval cortical inhibition (LICI). Generalization effects of anodal-tDCS significantly correlated with LICI disinhibition. CONCLUSION: Anodal-tDCS facilitates motor learning generalisation in an aging population through intracortical disinhibition effects. SIGNIFICANCE: The current findings demonstrate the potential clinical utility of a multisession anodal-tDCS over M1 protocol as an adjuvant to motor training in alleviating age-associated motor function decline. This study also reveals the pertinence of implementing brain stimulation techniques to modulate age-associated intracortical inhibition changes in order to facilitate motor function gains.

Failure of temporal selectivity: Electrophysiological evidence for (mis)selection of distractors during the attentional blink.

The attentional blink (AB) refers to the impairment in accurate report of a second target (T2) when presented shortly after a first target (T1) in a rapid serial visual presentation of distractors. The goal of the present study was to determine whether the AB is caused by a failure in early selection processes, which leads to the selection and consolidation of the wrong item in working memory, by measuring the frequency-related P3 to T2 and to T2 + 1. During the AB, an attenuation of the P3 to T2 was observed, as well as an increase in the amplitude of the P3 to T2 + 1. Whereas the P3 to T2 was observed only when T2 was correctly reported, the P3 to T2 + 1 was observed only in trials where T2 was incorrectly reported, and its amplitude was correlated to individual differences in misselection rate. These results support the claim that failure of temporal selection underlies the AB.

Electrophysiological correlates of motor sequence learning.

BACKGROUND: The Error-related negativity (ERN) is a component of the event-related brain potentials elicited by error commission. The ERN is thought to reflect cognitive control processes aiming to improve performance. As previous studies showed a modulation of the ERN amplitude throughout the execution of a learning task, this study aims to follow the ERN amplitude changes from early to late learning blocks in relation with concomitant motor sequence learning using a serial reaction time (SRT) task. Twenty-two healthy participants completed a SRT task during which continuous EEG activity was recorded. The SRT task consists of series of stimulus-response pairs and involves motor learning of a repeating sequence. Learning was computed as the difference in mean response time between the last sequence block and the last random blocks that immediately follows it (sequence-specific learning). Event-related potentials were analysed to measure ERN amplitude elicited by error commission. RESULTS: Mean ERN amplitude difference between the first four learning blocks and the last four learning blocks of the SRT task correlated significantly with motor sequence learning as well as with overall response time improvement, such that those participants whose ERN amplitude most increased through learning blocks were also those who exhibited most SRT task improvements. In contrast, neither sequence-specific learning nor overall response time improvement across learning blocks were found to be related to averaged ERN amplitude from all learning blocks. CONCLUSION: Findings from the present study suggest that the ERN amplitude changes from early to late learning blocks occurring over the course of the SRT task, as opposed to the averaged ERN amplitude from all learning blocks, is more closely associated with learning of a motor sequence. These findings propose an improved electrophysiological marker to index change in cognitive control efficiency during motor sequence learning.

Masking of a first target in the attentional blink attenuates the P3 to the first target and delays the P3 to the second target.

The attentional blink (AB) refers to the decline in report accuracy of a second target (T2) when presented shortly after a first target (T1) in a rapid serial visual presentation (RSVP) of distractors. It is known that masking T1 increases the magnitude of the AB, and masking a single target (equivalent to T1) in a RSVP stream attenuates the P3 to the target in correct trials. The major purpose of the present study was to clarify how these two effects may be integrated. An intervening distractor was presented at lag 1 (T1+1), at lag 2 (T1+2), or at neither of these two lags (no distractor). T2 was always presented at lag 3, as the last item in the stream. The P3 to T1 was attenuated and the P3 to T2 delayed in the T1+1 condition compared to the two other distractor conditions. These results clearly show that masking T1 attenuates the P3 to T1 and delays the P3 to T2 in the AB. Implications for extant theories of the AB are discussed.