Prefrontal hemodynamic changes produced by anodal direct current stimulation.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that has been investigated for the treatment of many neurological or neuropsychiatric disorders. Its main effect is to modulate the cortical excitability depending on the polarity of the current applied. However, understanding the mechanisms by which these modulations are induced and persist is still an open question. A possible marker indicating a change in cortical activity is the subsequent variation in regional blood flow and metabolism. These variations can be effectively monitored using functional near-infrared spectroscopy (fNIRS), which offers a noninvasive and portable measure of regional blood oxygenation state in cortical tissue. We studied healthy volunteers at rest and evaluated the changes in cortical oxygenation related to tDCS using fNIRS. Subjects were tested after active stimulation (12 subjects) and sham stimulation (10 subjects). Electrodes were applied at two prefrontal locations; stimulation lasted 10 min and fNIRS data were then collected for 20 min. The anodal stimulation induced a significant increase in oxyhemoglobin (HbO(2)) concentration compared to sham stimulation. Additionally, the effect of active 10-min tDCS was localized in time and lasted up to 8-10 min after the end of the stimulation. The cathodal stimulation manifested instead a negligible effect. The changes induced by tDCS on HbO(2), as captured by fNIRS, agreed with the results of previous studies. Taken together, these results help clarify the mechanisms underlying the regional alterations induced by tDCS and validate the use of fNIRS as a possible noninvasive method to monitor the neuromodulation effect of tDCS.

Symbol Digit Modalities Test: Normative data for the Latin American Spanish speaking adult population.

OBJECTIVE: To generate normative data on the Symbol Digit Modalities Test (SDMT) across 11 countries in Latin America, with country-specific adjustments for gender, age, and education, where appropriate. METHOD: The sample consisted of 3,977 healthy adults who were recruited from Argentina, Bolivia, Chile, Cuba, El Salvador, Guatemala, Honduras, Mexico, Paraguay, Peru, and, Puerto Rico. Each subject was administered the SDMT as part of a larger neuropsychological battery. A standardized five-step statistical procedure was used to generate the norms. RESULTS: The final multiple linear regression models explained 29-56% of the variance in SDMT scores. Although there were gender differences on the SDMT in Mexico, Honduras, Paraguay, and Guatemala, none of the four countries had an effect size greater than 0.3. As a result, gender-adjusted norms were not generated. CONCLUSIONS: This is the first normative multicenter study conducted in Latin America to create norms for the SDMT; this study will have an impact on the future practice of neuropsychology throughout the global region.

Trail Making Test: Normative data for the Latin American Spanish speaking adult population.

OBJECTIVE: To generate normative data on the Trail Making Test (TMT) across 11 countries in Latin America, with country-specific adjustments for gender, age, and education, where appropriate. METHOD: The sample consisted of 3,977 healthy adults who were recruited from Mexico, Argentina, Peru, Paraguay, Honduras, Chile, Cuba, Puerto Rico, Guatemala, El Salvador, and Bolivia. Each subject was administered the TMT as part of a larger neuropsychological battery. A standardized five-step statistical procedure was used to generate the norms. RESULTS: The final multiple linear regression models for the TMT-A explained 23- 50% of the variance, and the final multiple linear models for the TMT-B explained 22- 49% of the variance. Although there were gender differences on the TMT in Mexico, Peru, Paraguay, and Honduras, only Honduras had an effect size greater than 0.3. As a result, gender-adjusted norms were generated for the Trail Making Test-A, but not B, in this country. CONCLUSIONS: The present study is the first to create norms for the TMT in Latin America. As a result, this study will have important implications for the practice of neuropsychology in the future.

CB1 receptor antagonism/inverse agonism increases motor system excitability in humans.

CB1 receptor is highly expressed in cerebral structures related to motor control, such as motor cortex, basal ganglia and cerebellum. In the spinal cord, the expression of CB1 receptors has also been observed in ventral motor neurons, interneurons and primary afferents, i.e., in the cells that may be part of the circuits involved in motor control. It is known that the antagonist/inverse agonist of CB1 receptors Rimonabant penetrates the blood-brain barrier and produces a broad range of central psychoactive effects in humans. Based on the occurrence of central effects in humans treated with Rimonabant and on the location of CB1 receptors, we hypothesized that the application of Rimonabant can also affect the motor system. We tested the effects of a single dose of 20mg of Rimonabant on the excitability of motor cortex and of spinal motor neurons in order to detect a possible drug action on motor system at cortical and spinal levels. For this purpose we use classical protocols of transcranial magnetic and electrical stimulation (TMS and TES). Single and paired pulse TMS and TES were used to assess a number of parameters of cortical inhibition and cortical excitability as well as of the excitability of spinal motor neurons. We demonstrated that a single oral dose of 20mg of Rimonabant can increase motor system excitability at cortical and spinal levels. This opens new avenues to test the CB1R antagonists/inverse agonists for the treatment of a number of neurological dysfunctions in which can be useful to increase the excitability levels of motor system. Virtually all the disorders characterized by a reduced output of the motor cortex can be included in the list of the disorders that can be treated using CB1 antagonists/reverse agonists (e.g. stroke, traumatic brain injury, spinal cord injury, multiple sclerosis, fatigue syndromes, parkinsonisms, etc.).