Posts Tagged ‘Transcranial direct current stimulation’

Tools of Cognitive Neuroscience

September 10, 2019

The title of this post is identical to a chapter title in an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” The tools of cognitive neuroscience are highly technical. If the reader is interested in these techniques she should read Dr.Slotnick’s book, or look up the tools of interest in the Wikipedia.

One of the earliest techniques was positron emission tomography (PET). It required that a low level of radioactive material be injected into the participants bloodstream. This technique measured increased blood flow to the portions of the brain being activated. Fortunately a new technique that measured blood flow was found that did not require the injection of radioactive dye or any other type of material.

That technique was functional magnetic resonance imaging (fMRI), which also measured where in the brain the blood flow was increasing.

Event-related potentials (ERPs) can track brain activity in real time. ERPs directly measure neural activity and have a temporal resolution in milliseconds. Its spatial resolution is in centimeters, which is much lower than fMRI.

Electroencephalography (EEG) uses the identical data acquisition as ERPs, but refers to any measure of brain activity that corresponds to electric fields. This includes ERPs, but more commonly refers to brain activity that oscillates within a specific range of frequencies. EEG frequency analysis is a powerful alternative to the more commonly employed ERP analysis. Related to EEG, magnetoencephalography (MEG) refers to any measure of brain activity that corresponds to magnetic fields, and also typically refers to brain activity that oscillates within a specific frequency range. Like ERPs that are generated by averaging all the events of a given type from EEG data during a cognitive task, event-related fields (ERFs) are generated by averaging all the events of a given type from MEG data. The more general terms EEG and MEG also refer to ERPs and ERFs.

Dr. Slotnick writes, “fMRI is by far the most popular method in the field of cognitive neuroscience. However, brain activity is not a static set of blobs that represent a cognitive process. Rather, brain activity changes across different regions in milliseconds. Only techniques with excellent temporal resolution, such as ERPs, can track the functioning brain. This book highlights the temporal dimension of brain processing in addition to the spatial dimension of brain processing. One major advantage of temporal information is that one can use it to assess whether different brain regions are synchronously active, which indicates that these regions interact. This reflects how the brain is actually operating.”

Transcranial magnetic stimulation (TMS) can be used to temporarily disrupt processing in one region of the brain.

Transcranial direct current stimulation (tDCS) is similar to TMS in that it temp[orarily modulates processing in a target cortical region by stimulating with a weak direct current rather than a magnetic field.

A relatively new method called transcranial alternating current stimulation (tACS) uses the identical setup as tDCS, but the current alternatives at a specific frequency; this, tACS can stimulate the brain at a desired frequency.

Do not let yourself be discouraged or turned off by this technical stuff, but brief explanations are needed as these are the tools used in this research. The remainder of the posts will be on memory performance and on the portions of the brain contributing to this performance.

Using tDCS to Help Children with Developmental Disabilities and to Foster Creativity in Adults

August 19, 2012

An earlier Healthy Memory Blog Post, “Brain Boosts”, described means of boosting the brain’s performance. One of these was transcranial direct current stimulation (tDCS). The current is very small, from 1 to 2 milliamps. This method is much safer than other types of brain simulation as tDCS does not cause neurons to fire directly. It must make the neurons more excitable. When tDCS is applied over the right parietal lobe of the brain, mathematical ability is boosted. When it is applied to the right anterior temporal lobe, visual perception and memory is boosted.

An experiment examining enhancing mathematical ability was summarized in Scientific American Mind1 . Children with developmental dyscalia, a learning disability that affects math skill, served in the experiment. These children were to associate numbers with arbitrary symbols, such as triangles or cylinders. After practicing this task, they were rapidly presented with pairs of symbols of different visual sizes and they had to choose the physically larger one as quickly as they could. On some trials there was a mismatch between the size of the symbol and the magnitude it represented (for example a huge symbol meaning two was paired with a tiny symbol representing 5. Such mismatches could cause a delay in reaction because the impulse to choose the larger number needed to be overridden. The experimental group received tDCS over the right parietal cortex for 20 minutes at the beginning of each of the six training sessions. The control group did not receive the stimulation. By the fourth session the children in the experimental group became slower for mismatched pairs as compared with the matched pairs. This is the performance that adults show when they respond to real digits. The control group showed no difference between these trials suggesting that they had not internalized the symbols meaning. These superior performance lasted for six months, which suggests that this method might someday benefit those with developmental dyscalia.

In a special box2 inside her article on creativity in Scientific American Mind, Prof. Chrysikou of the University of Kansas reports on how tDCS, transcranial direct simulation can foster creativity. She reports a study published in 2011 by neuroscientist Allan Snyder of the Center for the Mind in Sydney in which Snyder and his colleagues used this technique to affect the ability of individuals to solve arithmetic puzzles involving matchsticks. The initial problems could all be solved with a similar strategy, but the approach would not work with the last two problems. These problems required a novel approach. For half the subjects tDCS was used to depress activity in the left frontal cortex, while exciting the right frontal cortex, whereas for the other half tDCS was used to excite activity in the left frontal cortex and depress activity in the right frontal cortex. The former group solved the last two problems at higher rates than the latter group. So it appears that the right hemisphere enhances creativity, whereas the left hemisphere impedes it.

Prof. Chrysikou also provided data that tDCS could also support the generation of novel ideas. She again used the method of suppressing one groups’ left prefrontal cortex while suppressing a second groups’ right prefrontal cortex. Yet a third group received sham simulation. The task was to think of novel uses of objects presented in pictures. The group receiving left prefrontal suppression thought of significantly more novel uses and did so significantly faster than the other two groups. These results support the notion that blocking the cognitive filter by inhibiting the left prefrontal cortex during idea generation can promote creative thought.

To the best of my knowledge tDCS is a research tool and not yet ready for prime time. If and when tDCS moves to practical applications remains an open question.

1Weaver, J. (2011). A Stimulating Solution for Math Problems. Scientific American Mind, March/April p.12

2Chrysikou, E.G. (2012). Tickling the Brain. Scientific American Mind, July/August, p. 29.