[show abstract][hide abstract] ABSTRACT: Introduction The study of human brain mechanism in cognitive science has become active recently due to the advancement of non-invasive brain measurement methods. In some experimental studies, reaction time tasks like button press have been used to analyze cognitive performance. However, few studies have been done to examine the human brain mechanism in the reaction time task. It has been reported in fMRI and PET studies that there are some differences in the motor activity between a self-paced movement (SPM) and an externally triggered movement (ETM) [1, 2]. Although there have been reported many MEG studies related to SPM [3, 4], not much is known about motor activity during ETM [5, 6]. By the way, it was recently reported that the primary motor cortex (MI) was not only structurally [7, 8] but also functionally inhomogeneous  and was differently activated depending on the task. It is important, not only for the motion control study but for the cognitive science, to examine the cha
[show abstract][hide abstract] ABSTRACT: The human primary motor cortex during a unilateral finger reactive movement to visual stimuli was examined by magnetoencephalography (MEG) measurement. The brain activity related to movement execution (the motor activity contralateral to the movement side) was estimated based on movement onset conditions and reaction times. The movement onset conditions were: (1) a simple reaction time task with a visual stimulus, (2) a Go/NoGo task with different colored stimuli and (3) a Go/NoGo task with different position stimuli. Dipole source estimation was done, and the time course of the motor activity was calculated. The results showed that not only the visual response but also the contralateral motor activity was evoked by the stimulus in all cases, and even when the NoGo stimulus was given. The motor activity in the primary motor cortex was conjectured to consist of two dominant components: the first component for the movement preparation and the second component for the movement execution. Because the first component happened with a constant delay time from the stimulus even in the NoGo case, the first component, coming through a fast pathway for signals from visual stimulus processing to the motor cortex without any intervening cognitive processing, was conjectured to make the motor cortex prepare for the forthcoming movement onset automatically regardless of the stimulus instruction.
Cognitive Brain Research 11/1999; 8(3):229-39. · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: Using magnetoencephalography (MEG) and a taste stimulator with rapid-rise time, we previously located the primary gustatory area in the human cerebral cortex and also investigated the relation between the onset latency of the gustatory-evoked magnetic fields (GEM) and reaction times (RT) in different taste qualities. In the present study, we investigated the temporal process from receptors to the higher brain in taste detection based on the results of the GEM and RT of different tastes. We used 100 mM, 300 mM and 1 M NaCl and 3 mM saccharine. The duration of each stimulus was 400 ms. The interstimulus interval was approximately 30 s. The temperature of both taste solution and deionized water was maintained the same as that of the tongue. Four subjects participated in this experiment. The 64-channel whole-head SQUID system (CTF Systems Inc., Canada) was used to measure GEM. The sampling rate was 250 Hz, and the low-pass filter was 40 Hz. In each subject, GEM and RT to a given taste were measured separately by applying 40 trials of stimulation. After each trial of both measurements, subjects showed a perceived intensity by using their fingers. In the GEM study, the trials contaminated with eye movements were rejected and the remaining trials were averaged. Averaged GEM were super-imposed on the same sheet with all 64 channels to measure the onset latency of GEM from the stimulus onset. RT and onset latencies of GEM were longer for saccharine than NaCl, and the value of RT minus the onset latency of GEM from RT, presumably indicating the time for higher brain process plus motor process, did not differ between 3 mM saccharine and 1 M NaCl. With increased concentrations of NaCl, RT became shorter, but onset latencies of GEM remained constant. Sweet taste took a longer time than salty taste at receptor process including the time for diffusion to receptors.
Annals of the New York Academy of Sciences 12/1998; 855:493-7. · 4.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: We investigated the spatio-temporal brain activity on the time scale of several milliseconds related to the mental rotation task requiring judgements of hand orientation, using a whole-cortex MEG (magnetoencephalography) system. Neuronal activity in the visual cortex was observed approximately 100-200 ms from stimulus onset, and that in inferior parietal lobe followed (after 200 ms). Both of these activities showed a contralateral dominance to visual stimulus hemifield. Premotor activity started later than the inferior parietal lobe activity, and these activities partially overlapped. Activity in primary motor and/or motosensory areas was observed in some subjects. The whole-cortex neuromagnetic measurements provided the time course of activity in the human brain associated with the implicit motor imagery: visual cortex-->inferior parietal lobe<-->premotor cortex. This process is considered to be the transformation process of retinotopic locations into a body-centered reference frame necessary for the mental rotation task.
[show abstract][hide abstract] ABSTRACT: We carried out multi-dipole estimation and pursued spatio-temporal brain activity on a time scale of several milliseconds during an auditory discrimination task using a whole-cortex type SQUID system. Neuronal activities were estimated in the medial (hippocampus, parahippocampal gyrus, etc.) and lateral temporal cortices (superior and middle temporal gyri, etc.), the dorsolateral prefrontal cortex (middle and inferior frontal gyri, etc.) and the parietal cortex (supramarginal gyrus, etc.) in the 280-400 ms latency range. The activity in the posterior hippocampal region was the most prominent and long-lasting in parallel with the activities in the other regions. Therefore, the posterior hippocampal region is a central structure engaged in auditory discrimination. The whole-cortex neuromagnetic measurements provided the possibility of imaging the time-varying activities of the human cortico-hippocampal neural networks.
[show abstract][hide abstract] ABSTRACT: Magnetic fields (MFs) from gustatory stimulation with 1 M NaCl and 3 mM saccharin were recorded from the human brain by using a whole-cortex SQUID system. The averaged onset latency of MFs was 93 ms for NaCI and 172 ms for saccharin and no response was obtained for water. A high correlation coefficient was noted between the difference of onset MFs latencies in two tastants and that of behavioral reaction times, and responses to saccharin were delayed or abolished after treatment of a subject's tongue with a sweet-suppressing agent. This finding indicates that the MFs obtained were caused by gustatory stimulation. By plotting the estimated current dipole on the magnetic resonance image, we could locate the primary gustatory area at the transition area between the operculum and insula, as reported in macaque monkeys.