Brain simulation techniques have demonstrated undisputable therapeutic effects on neural diseases. Invasive stimulation techniques like deep brain stimulation (DBS) and noninvasive techniques like transcranial magnetic stimulation (TMS) have been approved by FDA as treatments for many drug resist neural disorders and diseases. Developing noninvasive, deep, and targeted brain stimulation techniques is currently one of the important tasks in brain researches. Transcranial direct current stimulation (tDCS) and transcranial alternative current stimulation (tACS) techniques have the advantages of low cost and portability. However, neither of them can produce targeted stimulation due to lacking of electrical field focusing mechanism. Recently, Grossman et al. reported using the down beating signals of two tACS signals to accomplish focused stimulation. By sending two sine waves running at slightly different high frequencies (~2kHz), they demonstrated that they can modulate a “localized” neuron group at the difference frequency of the two sine waves and at the same time avoid excitation of neurons at other locations. As a result, equivalent focusing effect was accomplished by such beating mechanism. In this work, we show neither theoretically nor experimentally the beating mechanism can produce “focusing effect” and the beating signal spread globally across the full brain. The localized modulation effect likely happened right at the electrode contact sites when the electrode contact area is small and the current is concentrated. We conclude that to accomplish noninvasive and focused stimulation at current stage the only available tool is the focused TMS system we recently demonstrated.
This paper provides a comparative analysis of right handed people and left handed people when they write with both their hands. Two left handed and one right handed subject were asked to write their respective names on a paper using both, their left and right handed, and their brain signals were measured using EEG. Similarly, they were asked to perform simple mathematical calculations using both their hand. The data collected from the EEG from writing with both hands is compared. It is observed that though it is expected that the right brain only would contribute to left handed writing and vice versa, it is not so. When a right handed person writes with his/her left hand, the initial instinct is to go for writing with the right hand. Hence, both parts of the brain are active when a subject writes with the other hand. However, when the activity is repeated, the brain learns to expect to write with the other hand as the activity is repeated and then only the expected part of the brain is active.
Electroencephalography (EEG) is one of the most widely used electrophysiological monitoring methods and plays a significant role in studies of human brain electrical activities. Default mode network (DMN), is a functional connection of brain regions that are activated while subjects are not in task positive state or not focused on the outside world. In this study, EEG was used for human brain signals recording while all subjects were asked to sit down quietly on a chair with eyes closed and thinking about some parts of their own body, such as left and right hands, left and right ears, lips, nose, and the images of faces that they were familiar with as well as doing some simple mathematical calculation. The time is marker when the image is formed in the subject’s mind. By analyzing brain activity maps 300ms right before the time marked instant for each of the 4 wave bands, Delta, Theta, Alpha and Beta waves. We found that for most EEG datasets during this 300ms, Delta wave activity would mostly locate at the frontal lobe or the visual cortex, and the change and movement of activities are slow. Theta wave activity tended to rotate along the edge of cortex either clockwise or counterclockwise. Beta wave behaved like inquiry types of oscillations between any two regions spread over the cortex. Alpha wave activity looks like a mix of the Theta and Beta activities but more close to Theta activity. From the observation we feel that Beta and high Alpha are playing utility role for information inquiry. Theta and low Alpha are likely playing the role of binding and imagination formation in DMN operations.
Transcranial magnetic stimulation (TMS) has become one of the most widely used noninvasive method for brain tissue stimulation and has been used as a treatment tool for various neurological and psychiatric disorders including migraine, stroke, Parkinson's disease, dystonia, tinnitus and depression. In the process of developing advanced TMS deep brain stimulation tools, we need first to develop field measurement devices like sensory probes and brain phantoms, which can be used to calibrate the TMS systems. Currently there are commercially available DC magnetic or electric filed measurement sensors, but there is no instrument to measure transient fields. In our study, we used a commercial figure-8 shaped TMS coil to generate transient magnetic field and followed induced field and current. The coil was driven by power amplified signal from a pulse generator with tunable pulse rate, amplitude, and duration. In order to obtain a 3D plot of induced vector electric field, many types of probes were designed to detect single component of electric-field vectors along x, y and z axis in the space around TMS coil. We found that resistor probes has an optimized signal-to-noise ratio (SNR) near 3k ohm but it signal output is too weak compared with other techniques. We also found that inductor probes can have very high output for Curl E measurement, but it is not the E-field distribution we are interested in. Probes with electrical wire wrapped around iron coil can directly measure induced E-field with high sensitivity, which matched computer simulation results.
Bistable illusion reflects two different kinds of interpretations for a single image, which is currently known as a competition between two groups of antagonism of neurons. Recent research indicates that these two groups of antagonism of neurons express different comprehension, while one group is emitting a pulse, the other group will be restrained. On the other hand, when this inhibition mechanism becomes weaker, the other antagonism neurons group will take over the interpretation. Since attention plays key roles controlling cognition, is highly interesting to find the location and frequency band used by brain (with either top-down or bottom-up control) to reach deterministic visual perceptions. In our study, we used a 16-channel EEG system to record brain signals from subjects while conducting bistable illusion testing. An extra channel of the EEG system was used for temporal marking. The moment when subjects reach a perception switch, they click the channel and mark the time. The recorded data were presented in form of brain electrical activity map (BEAM) with different frequency bands for analysis. It was found that the visual cortex in the on the right side between parietal and occipital areas was controlling the switching of perception. In the periods with stable perception, we can constantly observe all the delta, theta, alpha and beta waves. While the period perception is switching, almost all theta, alpha, and beta waves were suppressed by delta waves. This result suggests that delta wave may control the processing of perception switching.
In a computer network there are distinct data channels and control channels where massive amount of visual information
are transported through data channels but the information streams are routed and controlled by intelligent algorithm
through “control channels”. Recent studies on cognition and consciousness have shown that the brain control channels
are closely related to the brainwave beta (14-40 Hz) and alpha (7-13 Hz) oscillations. The high-beta wave is used by
brain to synchronize local neural activities and the alpha oscillation is for desynchronization. When two sensory inputs
are simultaneously presented to a person, the high-beta is used to select one of the inputs and the alpha is used to
deselect the other so that only one input will get the attention. In this work we demonstrated that we can scan a person’s
brain using binaural beats technique and identify the individual’s preferred control channels. The identified control
channels can then be used to influence the subject’s brain executive functions. In the experiment, an EEG measurement
system was used to record and identify a subject’s control channels. After these channels were identified, the subject was
asked to do Stroop tests. Binaural beats was again used to produce these control-channel frequencies on the subject’s
brain when we recorded the completion time of each test. We found that the high-beta signal indeed speeded up the
subject’s executive function performance and reduced the time to complete incongruent tests, while the alpha signal
didn’t seem to be able to slow down the executive function performance.