Shoogo Ueno

Global and fine information coded by single neurons in the temporal visual cortex

When we see a persons face, we can easily recognize their species, individual identity and emotional state. How does the brain represent such complex information? A substantial number of neurons in the macaque temporal cortex respond to faces. However, the neuronal mechanisms underlying the processing ofcomplex information are not yet clear. Here we recorded the activity of single neurons in the temporal cortex of macaque monkeys while presenting visual stimuli consisting of geometric shapes, and monkey and human faces with various expressions. Information theory was used to investigate how well the neuronal responses could categorize the stimuli. We found that single neurons conveyed two different scales of facial information intheir firing patterns, starting at different latencies. Global information, categorizing stimuli as monkey faces, human faces or shapes, was conveyed in the earliest part of the responses. Fineinformation about identity or expression was conveyed later,beginning on average 51 ms after global information. We speculate that global information could be used as a ‘header’ to prepare destination areas for receiving more detailed information.

Localized stimulation of neural tissues in the brain by means of a paired configuration of time‐varying magnetic fields

A method of localized stimulation of the human brain is proposed. The basic idea is to concentrate induced eddy currents locally in the vicinity of a target in the cortex by a pair of coils which are positioned outside the head so that time‐varying magnetic fields pass through the head in the opposite directions around a target. The eddy currents induced at the target are expected to flow together, which results in an increased current flow at the target. Spatial distributions of induced eddy currents are calculated in cubical and spherical volume conductor models by a finite element method. The results show that the current vectors make themselves two vortexes which flow together at the target. The current density at the target makes a peak which is higher by 2–3 times than current densities at nontarget regions. The validity of the proposed method is demonstrated by experiments using frog nerve‐muscle preparations.

Strong Static Magnetic Field Stimulates Bone Formation to a Definite Orientation In Vitro and In Vivo

The induction of bone formation to an intentional orientation is a potentially viable clinical treatment for bone disorders. Among the many chemical and physical factors, a static magnetic field (SMF) of tesla order can regulate the shapes of blood cells and matrix fibers. This study investigated the effects of a strong SMF (8 T) on bone formation in both in vivo and in vitro systems. After 60 h of exposure to the SMF, cultured mouse osteoblastic MC3T3‐E1 cells were transformed to rodlike shapes and were orientated in the direction parallel to the magnetic field. Although this strong SMF exposure did not affect cell proliferation, it up‐regulated cell differentiation and matrix synthesis as determined by ALP and alizarin red stainings, respectively. The SMF also stimulated ectopic bone formation in and around subcutaneously implanted bone morphogenetic protein (BMP) 2‐containing pellets in mice, in which the orientation of bone formation was parallel to the magnetic field. It is concluded that a strong SMF has the potency not only to stimulate bone formation, but also to regulate its orientation in both in vitro and in vivo models. This is the first study to show the regulation of the orientation of adherent cells by a magnetic field. We propose that the combination of a strong SMF and a potent osteogenic agent such as BMP possibly may lead to an effective treatment of bone fractures and defects.

Properties of diamagnetic fluid in high gradient magnetic fields

This study focuses on the properties of diamagnetic fluid in static magnetic fields up to 8 T with the gradient of 50 T/m. We used a horizontal type of superconducting magnet with a bore 100 mm in diameter and 700 mm long. We observed the phenomenon that the surface of the water was pushed back by magnetic fields of higher gradients. Two ‘‘frozen’’ cascades were formed at z=±50–80 mm; the surface of the water near the center of the magnet was parted, and the bottom of the water chamber appeared. The water level at both ends of the chamber was lifted up. In order to investigate the hydrodynamics of diamagnetic fluid in magnetic fields, we made a fluidic circuit with plastic tubing which passed through the superconducting magnet’s bore. When magnetic fields in the center of the bore were changed from 0 to 8 T, the flow velocity of distilled water decreased, and the flow was stopped at 8 T. A stress analysis of diamagnetic fluid in magnetic fields was carried out to explain the mechanism of these phenomena. ...

Functional mapping of the human motor cortex obtained by focal and vectorial magnetic stimulation of the brain

Functional mapping of the human motor cortex related to the hand and foot area was carried out using focal magnetic stimulation of the brain. The basic idea of localized brain stimulation is to concentrate induced eddy currents locally in the vicinity of a target by a pair of opposing pulsed magnetic fields. A figure-eight coil was positioned outside the head so that time-varying magnetic fields could pass through the head in opposite directions around a target. It was observed that an optimum direction of stimulating currents for neural excitation exists in each functional area in the cortex. The functional maps of the brain were sensitive to change in the direction of the stimulating currents. The experimental results suggest that the direction of current vectors for neural excitation in magnetic brain stimulation reflects both the anatomical and the functional organization of neural fibers in the brain. >

Neuronal current distribution imaging using magnetic resonance

A new functional magnetic resonance imaging (fMRI) technique to visualize the distribution of neuronal currents in the human brain was developed Measurements of the internal magnetic field deformation caused by an electric current dipole in a phantom were performed using a method based on the microscopic magnetic resonance imaging technique. The minimal value of the current dipole moment detected by the present method was determined to be 90 nAm. The technique was applied to obtain maps of human brain activity by using motor and sensory stimulus paradigms. Measurements were made with an EPI sequence at 1.5 T. Intensity changes, resulting from causes other than neuronal currents, were eliminated by editing functional images obtained with field gradients of different polarities. MRI mapping of the neuronal currents in the brain during middle finger and thumb tapping was clearly obtained.

The effect of repetitive transcranial magnetic stimulation on long-term potentiation in rat hippocampus depends on stimulus intensity

We investigated the effect of repetitive transcranial magnetic stimulation (rTMS) on long-term potentiation (LTP) in the rat hippocampus. Rats were magnetically stimulated at a rate of 1000 pulses/day for 7 days by a round coil, in which the peak magnetic fields at the center of the coil were 0.75 and 1.00 T. LTP enhancement was observed only in the 0.75-T rTMS group, while no change was observed in the 1.00-T rTMS group. These results suggest that the effect of rTMS on LTP depends on the stimulus intensity.

Biological and morphological effects on the brain after exposure of rats to a 1439 MHz TDMA field

We investigated the effects of exposure to a 1439 MHz TDMA (Time Division Multiple Access) field, as used in cellular phones, on the permeability of the blood-brain barrier (BBB), on the morphological changes of the brain, and on body-mass fluctuations. Male Sprague-Dawley (SD) rats were divided into three groups of eight rats each. The rats in the EM(+) group, which had their heads arrayed in a circle near the central antenna of an exposure system, were exposed to a 1439 MHz field for one hour a day. The rats in EM(-) group were also in the exposure system, however, without high-frequency electromagnetic wave (HF-EMW) exposure. The animals in the control group were neither placed in the system nor exposed to HF-EMWs. The exposure period was two or four weeks. The energy dose rate peaked at 2 W/kg in the brain; the average over the whole body was 0.25 W/kg. The changes in the permeability of BBB were investigated by Evans blue injection method and by immunostaining of serum albumin. HF-EMWs had no effect on the permeability of BBB. The morphological changes in the cerebellum were investigated by assessing the degeneration of Purkinje cells and the cell concentration in the granular layer. No significant changes were observed in the groups of rats exposed to HF-EMWs for two or four weeks. Averaged body masses were not affected by HF-EMWs exposure. In conclusion, a 1439 MHz TDMA field did not induce observable changes in the permeability of the BBB, morphological changes in the cerebellums, or body mass changes in rats, as evaluated by the conventional methods.

Asymmetries of prefrontal cortex in human episodic memory: effects of transcranial magnetic stimulation on learning abstract patterns.

Functional neuroimaging suggests asymmetries of memory encoding and retrieval in the prefrontal lobes, but different hypotheses have been presented concerning the nature of prefrontal hemispheric specialization. We studied an associative memory task involving pairs of Kanji (Chinese) pictographs and unfamiliar abstract patterns. Subjects were ten Japanese adults fluent in Kanji, so only the abstract patterns represented novel material. During encoding, transcranial magnetic stimulation (TMS) was applied over the left and right dorsolateral prefrontal cortex (DLPFC). A significant (P<0.05) reduction in subsequent recall of new associations was seen only with TMS over the right DLPFC. This result suggests that the right DLPFC contributes to encoding of visual-object associations, and is consistent with a material-specific rather than a process-specific model of mnemonic function in DLPFC.

Comparison of current distributions in electroconvulsive therapy and transcranial magnetic stimulation

We compared current density distributions in electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS) by numerical calculations. The model consisted of an air region and three types of tissues with different conductivities representing the brain, the skull, and the scalp. In the ECT model, electric currents were applied through electrodes with a voltage of 100 V. In the TMS model, a figure-eight coil (6 cm diameter per coil) was placed on the vertex of the head model. An alternating current with a peak intensity of 3.0 kA and a frequency of 4.2 kHz was applied to the coil. The maximum current densities inside the brain in ECT (bilateral electrode position) and TMS were 234 and 322 A/m2, respectively. The results indicate that magnetic stimulators can generate comparable current densities to ECT. While the skull significantly affected current distributions in ECT, TMS efficiently induced eddy currents in the brain. In addition, TMS is more beneficial than ECT because the localized curren...