Michela Brambilla

Enhancing verbal episodic memory in older and young subjects after non-invasive brain stimulation

Memory is the capacity to store, maintain, and retrieve events or information from the mind. Difficulties in verbal episodic memory commonly occur in healthy aging. In this paper, we assess the hypothesis that anodal transcranial direct current stimulation (tDCS) applied over the dorsolateral prefrontal cortex (DLPFC) or over the parietal cortex (PARC) could facilitate verbal episodic memory in a group of 32 healthy older adults and in a group of 32 young subjects relative to a sham stimulation using a single-blind randomized controlled design. Each participant underwent two sessions of anodal tDCS (left and right) and one session of sham stimulation. Overall, our results demonstrated that, in young and in older subjects, anodal tDCS applied during the retrieval phase facilitates verbal episodic memory. In particular, we found that tDCS applied over the left and right regions (DLPFC and PARC) induced better performance in young participants; only tDCS applied over the left regions (DLPFC and PARC) increased retrieval in older subjects. These results suggest that anodal tDCS can be a relevant tool to modulate the long-term episodic memory capacities of young and older subjects.

Anodal tDCS during face-name associations memory training in Alzheimer's patients

Objective: Given the limited effectiveness of pharmacological treatments, non-pharmacological interventions to treat Alzheimers disease (AD) have gained attention in recent years. The aim of the present study is to investigate the effects of anodal tDCS (AtDCS) combined with memory training on face-name associations in an AD patient sample. Methods: Thirty six AD patients were randomly assigned to one of three study groups: Group 1, AtDCS plus individualized computerized memory training; Group 2, placebo tDCS plus individualized computerized memory training; Group 3, AtDCS plus motor training. Results: A general improvement in performance was observed after 2 weeks of memory training. Both the anodal tDCS plus individualized computerized memory training and the placebo tDCS plus individualized computerized memory training groups had significantly improved performances at 2 weeks compared with the AtDCS plus motor training group. Conclusion: Our findings suggest a beneficial effect of individualized memory rehabilitation in AD patients.

The timing of cognitive plasticity in physiological aging: a tDCS study of naming.

This study aimed to explore the effects of transcranial direct current stimulation (tDCS) on physiologically aging adults performing a naming task. tDCS is a method that modulates human cortical excitability. Neuroplasticity is considered to have its foundation in cortical excitability as a property that adjusts the connection strength between neurons in the brain. Language efficiency, as all functions, relies on integration of information (i.e., effectiveness of connectivity) through neurons in the brain. So the use of tDCS, to modulate cortical excitability, can help to define the state of cognitive plasticity in the aging brain. Based on Hebbs rule, an increase in synaptic efficacy does not rely only on the increase of excitability but also on the timing of activation. Therefore, a key issue in this study is the timing of tDCS application in relation to a task: When to deliver tDCS to induce modulatory effects on task execution to facilitate naming. Anodal tDCS was applied to the left dorsolateral prefrontal cortex of older and young adults before and during a naming task. In older adults, tDCS improved naming performance and decreased the verbal reaction times only if it was applied during the task execution, whereas in young subjects both stimulation conditions improved naming performance. These findings highlight that in healthy aging adults, the cerebral network dedicated to lexical retrieval processing may be facilitated only if stimulation is applied to an “active” neural network. We hypothesize that this change is due to the neuronal synaptic changes, in the aging brain, which reduce the window of when cortical excitability can facilitate synaptic efficacy and therefore plasticity.

Noninvasive stimulation of prefrontal cortex strengthens existing episodic memories and reduces forgetting in the elderly

Memory consolidation is a dynamic process. Reactivation of consolidated memories by a reminder triggers reconsolidation, a time-limited period during which existing memories can be modified (i.e., weakened or strengthened). Episodic memory refers to our ability to recall specific past events about what happened, including where and when. Difficulties in this form of long-term memory commonly occur in healthy aging. Because episodic memory is critical for daily life functioning, the development of effective interventions to reduce memory loss in elderly individuals is of great importance. Previous studies in young adults showed that the dorsolateral prefrontal cortex (DLPFC) plays a causal role in strengthening of verbal episodic memories through reconsolidation. The aim of the present study was to explore the extent to which facilitatory transcranial direct current stimulation (anodal tDCS) over the left DLPFC would strengthen existing episodic memories through reconsolidation in elderly individuals. On Day 1, older adults learned a list of 20 words. On Day 2 (24 h later), they received a reminder or not, and after 10 min tDCS was applied over the left DLPFC. Memory recall was tested on Day 3 (48 h later) and Day 30 (1 month later). Surprisingly, anodal tDCS over the left DLPFC (i.e., with or without the reminder) strengthened existing verbal episodic memories and reduced forgetting compared to sham stimulation. These results provide a framework for testing the hypothesis that facilitatory tDCS of left DLPFC might strengthen existing episodic memories and reduce memory loss in older adults with amnestic mild cognitive impairment.

Mild cognitive impairment in Parkinson's disease is improved by transcranial direct current stimulation combined with physical therapy

Parkinsons disease (PD) is characterized by both motor and cognitive deficits. In PD, physical exercise has been found to improve physical functioning. Recent studies demonstrated that repeated sessions of transcranial direct current stimulation led to an increased performance in cognitive and motor tasks in patients with PD.

Prefrontal cortex rTMS enhances action naming in progressive non‐fluent aphasia

Background and purpose: Progressive non‐fluent aphasia (PNFA) is a neurodegenerative disorder that is characterized by non‐fluent speech with naming impairment and grammatical errors. It has been recently demonstrated that repetitive transcranial magnetic stimulation (rTMS) over the dorsolateral prefrontal cortex (DLPFC) improves action naming in healthy subjects and in subjects with Alzheimer’s disease.

Efficacy of semantic-phonological treatment combined with tDCS for verb retrieval in a patient with aphasia.

Recent studies reported enhanced performance on language tasks induced by transcranial direct current stimulation (tDCS) in patients with aphasia. One chronic patient with non-fluent aphasia received 20 sessions of a verb anomia training combined with off-line bihemispheric tDCS applied to the dorsolateral prefrontal cortex (DLPFC) – anodal tDCS over left DLPFC plus cathodal tDCS over right DLPFC. A significant improvement in verb naming was observed at all testing times (4, 12, 24, and 48 weeks from post-entry/baseline testing) for treated and untreated verbs. Our findings show beneficial effects of verb anomia training in combination with tDCS in chronic aphasic patient, suggesting a long-lasting effect of this treatment.

Action and Object Naming in Physiological Aging: An rTMS Study

Word-retrieval difficulties commonly occur in healthy aging. Recent studies report an improved ability to name pictures after the administration of high-frequency repetitive transcranial magnetic stimulation (rTMS) in healthy younger adults and in patients with neurological disease. The aim of this study was to assess the effect of high-frequency rTMS applied to the dorsolateral prefrontal cortex (DLPFC) on picture naming in healthy older adults. High-frequency rTMS was applied to the left and right DLPFC during object and action naming in 13 healthy older adults. The naming latency for actions was shortened after stimulation of the left and right DLPFC compared to application of the sham stimulation. Stimulation was not observed to have any effect on correctness of naming. Our data demonstrate the involvement of the left and right DLPFC in a sample of healthy aging subjects during an action-naming task. The bilateral involvement of the DLPFC in these participants is discussed together with data on younger adults and on Alzheimers patients.

Naming Ability Changes in Physiological and Pathological Aging

Over the last two decades, age-related anatomical and functional brain changes have been characterized by evidence acquired primarily by means of non-invasive functional neuroimaging. These functional changes are believed to favor positive reorganization driven by adaptations to system changes as compensation for cognitive decline. These functional modifications have been linked to residual brain plasticity mechanisms, suggesting that all areas of the brain remain plastic during physiological and pathological aging. A technique that can be used to investigate changes in physiological and pathological aging is non-invasive brain stimulation (NIBS). The present paper reviews studies that have applied NIBS in younger and older adults and in patients with dementia to track changes in the cerebral areas involved in a language task (naming). The results of this research suggest that the left frontal and temporal areas are crucial during naming. Moreover, it is suggested that in older adults and patients with dementia, the right prefrontal cortex is also engaged during naming tasks, and naming performance correlates with age and/or the degree of the pathological process. Potential theories underlying the bilateral involvement of the prefrontal cortex are discussed, and the relationship between the bilateral engagement of the prefrontal cortex and the age or degree of pathology is explored.

Time up and go task performance improves after transcranial direct current stimulation in patient affected by Parkinson's disease.

Locomotor disturbances represent one of the major distress in everyday life in people with Parkinsons disease (PD). Timed up and go test (TUG) has been advocated a useful and reliable tool for quantifying locomotor performance. The aim of this study was to assess the effect of anodal transcranial direct current stimulation (tDCS) applied over the dorsolateral prefrontal cortex (DLPFC) during timed up and go test (TUG) in a group of patients with PD. Ten participants underwent two sessions of anodal tDCS (left and right) and one session of placebo tDCS. TUG was performed before and after each tDCS session (anodal or placebo). A significant motor improvement after right DLPFC stimulation vs. placebo stimulation was observed. These results suggest that anodal tDCS can be a relevant tool to modulate walking abilities in PD.