stimulated, while they were stronger with compression than withdecompression when the 1st or 5th finger was stimulated.Although it has been stated the cortical area is much larger forthe 1st finger than for the 2nd or 5th finger (Penfield and Boldrey,1937), it appears that in terms of function the primary somatosen-sory cortex for the 2nd finger reacts differently than the cortex forthe 1st finger or 5th finger.

doi:10.1016/j.clinph.2008.01.056

32. The changes of somatosensory-evoked potentials pre-

ceded by contralateral median nerve stimulation in sleep—

Hiroshi Shimizu, Thoru Yamada, Tatsuya Abe, ShujiMatsumoto, Motohiko Hara, Hiroo Ichikawa, Toshio Soma,

Reiko Fujisawa, Shinichiro Taniguchi, Jun Kimura Univer-

sity of Iowa, Iowa City, USA)

The aim of this study was to determine if there is any inter-hemispheric interaction in somatosensory-evoked potentials(SEPs) by using condition (SI) and test (SII) paired stimulus par-adigm. This was examined during both wakefulness and sleep.The SI stimuli were delivered to right median nerve (MN) andSII stimuli were to left MN, with interstimulus interval (ISI) of0, 5, 10, 20, 50, 100 and 200 ms. Three stimulus modalities (SI,SII, SI + SII) were delivered in cyclic fashion throughout theawake and asleep states. SEPs were obtained as of off-line aftergrouping the responses according to the wakefulness and sleepstages of II, III/IV and REM. Control SEP showed decreasedamplitude of parietal N32–P40 and P40–N60 and increasedamplitude of frontal N19–P22 in non-REM sleep as comparedto those of wakefulness. The latencies of all peaks (except forP14) were prolonged with greater degree in later components.All these changes returned close to wakefulness during REMsleep. The test response also showed parallel changes with thecontrol responses throughout all ISIs both in wakefulness andsleep. It is concluded that there is no significant inter-hemisphericinteraction in sensory input between two hemispheres during bothwakefulness and sleep.

doi:10.1016/j.clinph.2008.01.057

33. Differences of EEG change in implicit and explicit

memory tasks—Tomoka Kobayashi, Masumi Inagaki,Kouta Suzuki, Makiko Kaga Department of Developmental

Disorders, NCNP, Kodaira, Japan)

The aim of this study was to neurophysiologically distinguishimplicit memory and explicit memory function. Black and whitedrawings of simple objects which were easily identified by pre-school children were used in the memory tasks. Subjects were14 young healthy adults whose average age was 22 years old. Adecision making task whether a picture matched a category wasused for assessing implicit memory function. Explicit memoryfunction was assessed by a recollection task after giving instruc-tions to memorize 30 given pictures. We recorded EEGs usingthe 128 channel Net Station System (Electrical Geodesics, Inc.).In the implicit memory task, there were positive waves with vertexdominancy, with a peak latency around 550–650 ms after stimu-

lus, which were larger for old pictures. On the other hand, inthe explicit memory task, there were Cz–Pz dominant negativewaves around 900 ms after stimulus. Our findings suggest thatimplicit and explicit memory might be clearly distinguishedthrough event-related brain potential studies.

doi:10.1016/j.clinph.2008.01.058

34. The Relationships between difficulty of the manual con-

trols and ERP—Yohei Shoji, Daiji Kobayashi, Sakae

Yamamoto Tokyo University of Science, Tokyo, Japan)

Operators control operational devices with the forecasting theposition of the target. This control system was called the predic-tive control. There are few studies which evaluate an operator atthe time of the prediction control physiologically. The purposeof this study is to investigate the variation of the negative ampli-tude in movement-related cortical potential (MRCP) when adegree of difficulty of the prediction control is high. Subjectscontrol the target to pass through gates by steering wheel oper-ation by their right arm. Three delay conditions of the experi-mental system are set it with a time constant. The experimentperforms 300 trials (each condition performed 100 trials at ran-dom). The EEGs are analyzed before and after 5000 ms of steer-ing operation. The subjects are 20 male students. Writteninformed consent was obtained from all participants. Individualdifference of electrical current potential was excluded by stan-dardization. The present results show that the negative compo-nents of MRCP over the left hemisphere in the condition witha time constant of 6 s are significantly greater than two othertime constant conditions. The results suggests that MRCP mayevaluate the degree of difficulty of the movement problem inthe rehabilitation therapy.

doi:10.1016/j.clinph.2008.01.059

35. Classification of movement imagery on the basis of sin-

gle-trial EEGs—Hideyuki Maki, Toshimasa Yamazaki,

Hiroshi Takayanagi, Takahiro Yamanoi, Ken-ichi Kamijo

Japan Technical Software Co., Ltd, Yokohama, Japan)

As the first step to develop a new brain-computer interface(BCI) using single-trial EEGs, we applied the independent compo-nent analysis (ICA), the equivalent current dipole source localiza-tion (ECDL), and then the classification by Hayashi’squantification method II to EEGs measured during movementimageries. This is a single case study. Up to the 20th independentcomponent, each of them contained one or two positive (or neg-ative) peaks in terms of 32-channel EEGs reconstructed on theelectrode surface by the deflation procedure. These peaks wereanalyzed by 1- or 2-dipole ECDL. Dipoles were fitted withinthe contralateral motor and premotor cortices regardless of theirtime course when a subject imaged single-handed movement.Moreover, the quantification method yielded a good discrimina-tion between left- and right-hand movement imageries.

doi:10.1016/j.clinph.2008.01.060

Japanese Society of Clinical Neurophysiology / Clinical Neurophysiology 119 (2008) e75–e93 e83