Posts Tagged ‘transcranial alternating 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.