CHICAGO—Transcranial direct current stimulation (tDCS) improves cognitive functioning in patients with Alzheimer’s disease and poststroke aphasia, according to the results of two studies reported at the 60th Annual Meeting of the American Academy of Neurology.
“Previous studies have shown that tDCS induces prolonged functional changes in the cerebral cortex due to synaptic and nonsynaptic mechanisms,” said Alberto Priori, MD, PhD. “Both Alzheimer’s disease and poststroke aphasia are characterized by dysfunction of specific cortical areas. The ability of a single tDCS session to focally modulate cortical function prompted us to assess the effect of this technique on these different clinical settings.”
tDCS Improves Picture Naming in Patients With Aphasia
Prof. Priori, who teaches Clinical Neurology and Neurophysiology in the Department of Neurological Sciences at the University of Milan Medical School, in collaboration with Filippo Cogiamanian, MD, and colleagues, assessed the effect of tDCS in damaged left frontotemporal areas of patients with chronic poststroke aphasia. Eight right-handed patients (mean age, 60) with poststroke aphasia were asked to complete a computer-controlled picture-naming task before and after anodal, cathodal, or sham tDCS of the left frontotemporal area.
In the first experiment, patients were assigned to an anodal tDCS group (four subjects) or a cathodal tDCS group (four subjects). The first group underwent anodal and sham tDCS over the left frontotemporal areas, whereas the second group underwent cathodal and sham tDCS. Active (anodal or cathodal) and sham tDCS were tested in random order, and at least one week elapsed between sessions. Because two subjects in the anodal tDCS group and two subjects in the cathodal tDCS group “were stimulated with inverted polarity, in total, six patients underwent anodal tDCS/sham tDCS in two separate sessions, and six patients underwent cathodal tDCS/sham tDCS in two separate sessions,” explained the researchers. To assess the specificity of the results, two months later all participants underwent cathodal and sham tDCS of the occipital cortex. tDCS (2 mA for 10 minutes) was delivered by a constant current stimulator to the selected areas.
During each picture-naming session, patients were asked to name pictures presented on a personal computer screen from one of four lists; each list contained 20 items. A score of 1 was assigned to each correct answer, while a score of 0 was assigned to each incorrect answer. Mean response time was also recorded.
According to the researchers, anodal tDCS of the left frontotemporal area was not associated with significant changes. Cathodal tDCS of this area significantly improved the accuracy of the naming task; moreover, tDCS of the occipital cortex did not affect the accuracy of naming, suggesting a polarity and site-specific effect of the stimulation.
Cognitive Effects of tDCS in Patients With Alzheimer’s Disease
In another study, Prof. Priori, along with Roberta Ferrucci, PsyD, and colleagues, evaluated the effect of tDCS over temporoparietal cortical areas, which are involved in recognition memory, in 10 patients with probable Alzheimer’s disease. Anodal, cathodal, and sham tDCS were tested in random order, during three separate experimental sessions at intervals of at least one week. Anodal and cathodal tDCS were delivered at a current intensity of 1.5 mA for 15 minutes.
Cognitive tasks were administered to patients before and 30 minutes after tDCS. Recognition memory was assessed with a pencil-and-paper word recognition task that required subjects to read loudly and remember a list of 12 words, then recognize them within a list of 24 words. Visual attention was assessed with an exogenous cue version of the Posner paradigm. “Patients responded to targets that appeared at one of two locations on either side of the fixation mark. Before the target appeared, one of these locations was cued so that subjects focused their attention on this location,” stated the researchers.
After anodal tDCS, the accuracy of the word recognition task significantly increased by 17%; cathodal tDCS was associated with decreased accuracy, and sham tDCS did not have any effect. In addition, tDCS did not affect visual attention reaction times.
“Because anodal tDCS increases cortical excitability and focally improves cortical function, it presumably improved our patients’ performance in the word recognition task test by focally improving the function of temporoparietal areas,” the investigators concluded.
A Simple, Safe, and Inexpensive Technique
Findings from both studies suggest that tDCS is a simple, safe, and inexpensive noninvasive brain stimulation technique, noted the researchers. “Our preliminary data on aphasic and Alzheimer’s disease patients are promising, as we observed beneficial effects after a single tDCS session, suggesting that chronic daily application might induce even greater improvement,” Prof. Priori commented.
Broader research programs using different stimulation protocols and longer clinical follow-up to clarify the impact that therapy might have on patients’ daily functioning are needed, said Prof. Priori. He plans to examine the long-lasting effects of tDCS in patients with poststroke aphasia and Alzheimer’s disease using repeated session protocols in a larger sample of patients.