Novel Technique for Noninvasive Detection of Localized Dynamic Brain Signals by Using Transcranial Static Magnetic Fields.

The techniques for noninvasive measurement of brain function such as electroencephalography (EEG), magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS) have been used in diagnosing brain conditions. However, the conventional techniques have critical limitations of spatial or temporal resolution. Here, we developed a novel technique which enables the precise measurement of dynamic brain signals and localized identification of active brain regions. In this technique, termed as magnetically biased field (MBF), human brain signal is measured as the fluctuation of a transcranial static magnetic field emitted by a coil placed on the scalp. The validity of MBF was confirmed by the measurement of somatosensory evoked signals. Fast somatosensory evoked signals were successfully observed. Localized maximum positive and negative deflections appeared at the region which represents the right primary somatosensory area contralateral to the stimulated hand. The ability of MBF to detect dynamic brain activity precisely can have numerous applications such as diagnosing brain diseases and brain-machine interfaces.

Noninvasive measurement of dynamic brain signals using light penetrating the brain.

Conventional techniques for the noninvasive measurement of brain activity involve critical limitations in spatial or temporal resolution. Here, we propose the method for noninvasive brain function measurement with high spatiotemporal resolution using optical signals. We verified that diffused near-infrared light penetrating through the upper jaw and into the skull, which we term as optoencephalography (OEG), leads to the detection of dynamic brain signals that vary concurrently with the electrophysiological neural activity. We measured the OEG signals following the stimulation of the median nerve in common marmosets. The OEG signal response was tightly coupled with the electrophysiological response represented by the somatosensory evoked potential (SSEP). The OEG measurement is also shown to offer rather clear discrimination of brain signals.

Inhibitory interference to abandonment of voluntary finger movement by single-pulse transcranial magnetic stimulation.

Brain function dynamics related to an inhibitory interference in voluntary motor abandonment was investigated with single-pulse transcranial magnetic stimulation (TMS) and electroencephalogram (EEG). As the voluntary motor movement, a point-to-point reaching movement of the right index-finger was conducted. The starting time of the movement was indicated with the clock making one revolution for 4 s. The time the clock hand passed the 9 o'clock position was defined as a go-signal. In the go trials, the subject was instructed to start the movement at the timing of the go signal. In some trials, called as pre-stop trials, a stop signal was presented with red LED illumination -100 ms from the timing of the go-signal. The go-trials and pre-stop trials were randomly performed in the series of the trials. In all trials, TMS or sham-TMS were conducted. TMS was delivered with a round coil on the subject's head at various timings. Sham-TMS trials were with a click sound of TMS produced by another coil located near the head without the brain stimulation. In the sham-TMS trials of the pre-stop trials, the subject was able to prevent the finger movement. However, the TMS conducted at -150, -100 or -50 ms from the go-signal induced the involuntary finger movement in the pre-stop trials. We also measured brain potentials in the sham-TMS and TMS trials. The potential at Fz electrode showed a large positive peak in the sham-TMS trials of the pre-stop trials, whereas the potentials at the same latency were attenuated in the TMS trials of the pre-stop trials. These results indicated that the single-pulse TMS applied around the stop-signal in the reaching finger movement could intervene in the brain function of the voluntary motor abandonment conducted at medial frontal cortex.

Brain activity evoked by motor inhibition before volitional finger movement.

The present study investigated the brain activity that accompanied motor inhibition before movement in human volitional finger movement. Seven individuals were instructed to press a force sensor with the right index finger. The time to begin this movement was indicated with a clock making a 4-s revolution. The time at which the clock hand passed the 3 o'clock position was adopted as the go-signal in the go task. In the series of trials, the task, we designated as prestop task, was performed with a red light-emitting diode stop-signal presented randomly at 0.1, 0.2, 0.3, 0.4, or 0.5 s before the go-signal. Cerebral potentials from the scalp were recorded using a 20-channel electroencephalography system. In the go task without the stop-signal, clear movement-related cortical potentials were observed. In the prestop tasks with the stop-signal, the participants were able to inhibit finger movement. A positive electroencephalography potential distributed at the midline frontocentral scalp 400 ms after the stop-signal was observed only in the prestop task. This suggests that the observed positive component is associated with the interruption of motor intent, as well as the revision of motor planning, in the motor cortices before the movement.

Control of reaching finger movement accompanied with inhibitory intention.

In the present study, we investigated the motor control of reaching finger movement interfered by the inhibitory intention triggered by the stop-signal. In the experiment, the subject started the reaching movement of the index finger with the go-signal of a green LED and stopped the ongoing movement with the stop-signal of a red LED. The stop-signal delay (SSD) was set at 0, 100, 200, 300 and 400 ms. The movement trajectory was measured during the task. The index finger was able to stop prior to the target point when SSD was less than 400 ms, whereas not when SSD was 400 ms. We also measured electroencephalogram (EEG) during the task. A negative peak around the stop-signal response time (SSRT) and a positive peak around 400-600 ms of the event-related potentials (ERPs) were observed at Fz and Cz. These results indicate that these components of the ERPs were associated with the stop-signal task in the human reaching movement.

EEG source estimation method considering the shape of the cortical surface.

The precision of current source estimation of electroencephalography by referring the shape of the brain acquired as MRI was considered. The location of the candidate current dipoles was limited to on the surface of the cortex, and the orientation was constrained to the vertical to the surface. Electric stimulation of median nerve was executed to confirm whether it works appropriately by checking the estimated active area on the cortex.