Dipole source localization of MEG by BP neural networks

Summary The purpose of this study was to examine the usefulness of BP neural networks for source localization of MEG. Since the performance of this method does not depend on the complexity of brain parameters and source models, a homogeneous brain model and a single current dipole source are assumed for convenience. Localization accuracy was examined in relation to the configuration and scale of the network. As a result, average error for position and moment estimations was within 2%, while the maximum error was about 5%. It was therefore concluded that the neural network method was useful for MEG source localization, though some improvements are still necessary.     

Inverse relationship of the velocities of perceived time and information processing events in the brain: A potential bioassay for neural functions: A hypothesis

The velocity of elapsing time is not a constant but a relativistic component in the space-time continuum as postulated by Albert Einstein in his general and special relativity theories. The hypothesis presented here is that there is a biological corollary to relativity theory. It is postulated that biological time perception is also not a constant but is related by an inverse relationship between the velocities of neural processing events and perceived elapsing time. A careful analysis of this relationship may potentially offer a sensitive bioassay to determine the integrity of regional brain function under normal conditions and in the presence of specific disease processes. The mechanism for the biological basis of this theorem depends on the presence of a neural circuit developed through evolution which monitors overall brain efficiency and is coordinately linked to neural time perceiving circuits. Several test approaches are presented to validate the hypothesis of biologic time relativity compared to the rate of neural processing.     

Generators of visual evoked potentials for faces and eyes in the human brain as determined by dipole localization

Human visual evoked potentials were recorded during presentation of photos of human and animal faces and various face features. Negative waves with approximate peak latencies of 165 msec (N170) were bilaterally recorded from the occipito-temporal regions. Mean peak latencies of the N170 were shorter for faces than eyes only. Analyses of amplitudes of evoked potentials indicated that the N170 elicited by faces reflected activity of a specific neural system which was insensitive to detailed differences among individual faces regardless of species, and consequently suggest that this system might function to detect existence of faces in general. On the other hand, the mean amplitude of the N170 elicited by human eyes was significantly larger than those by animal eyes. These differences in response latencies and amplitudes of the N170 suggest existence of at least 2 different visual evoked potentials with similar latencies (i.e., N170) which are sensitive to faces in general and human eyes, respectively. Dipole source localization analysis indicated that dipoles for the N170 elicited by eyes were located in the posterior inferior temporal gyrus, and those for faces, located initially in the same region, but moved toward the fusiform and lingual gyri at the late phase of the N170. The results indicated that information processing of faces and eyes separated at least as early as the latency of the N170 at the posterior inferior temporal gyrus as well as the fusiform and lingual gyri, and might provide neurophysiological and anatomical bases to an initial structural encoding stage of human faces.