Cerebral somatosensory potentials evoked by posterior tibial nerve stimulation: lateralization and relation to handedness in left-handed normal subjects

Event-related potentials during auditory oddball, and combined auditory oddball-visual paradigms

The purpose of the current study was to investigate the properties of a new modification of the classical auditory oddball paradigm (auditory oddball paradigm combined with passive visual stimulation, AERPs + VEPs) and compare the scalp topography obtained with the new paradigm and the classical auditory oddball paradigm (AERPs) in healthy humans. The responses to bimodal stimulation, and to the classical oddball paradigm were similar to those reported in other studies in terms of location, amplitudes, and latencies of P1, N1, P2, N2, and P300. The new modification of the oddball paradigm produced P300 at fronto-central locations in contrast to centro-parietal locations during the classical oddball paradigm. The amplitudes and latencies of P300 were also significantly larger during the new than the classical paradigm. Furthermore, the amplitudes of N1 and P2, but not N2 were significantly higher and differed in location during the new paradigm in response to both target and standard stimuli. The latencies of all three waves were significantly longer and the latency of P2 differed in location between the new and the classical paradigms in response to only the standard stimuli. The results of this study suggest that the new modification of the classical oddball paradigm produces different neural responses to the classical oddball paradigm. Therefore, this modification can be used to investigate dysfunctions in sensory and cognitive processing in clinical samples.

Visual evoked potentials in multiple sclerosis before and after two years of interferon therapy

Magnetic resonance imaging (MRI) is important in the diagnosis of and follow-up for the treatment of multiple sclerosis (MS); evoked potentials may be important if MRI is normal or cannot be performed. We assessed serial visual evoked potentials (VEPs) and cranial MRI in a group of clinically relapsing-remitting multiple sclerosis (N = 15) treated with interferon beta-lb (INFB-1b) and in normal subjects (N = 15). The investigations were done 1 week before INFB-lb therapy, 1 year later (N = 15), and 2 years later (N = 10). VEPs were abnormal in most of the patients; MRIs were abnormal in all patients. We used P100 latency as an electrophysiological index for the progress of illness. There were significant differences in VEPs between the beginning and ending of the interferon treatment. We concluded that VEPs would be a reliable index for following up the progress of MS under interferon therapy.

Somatosensory evoked potential and histopathological investigations in ischaemia-induced brain damage: effects of trimetazidine in rats

We studied the protective effects of trimetazidine (TMZ) on brain damage by means of somatosensory evoked potentials (SEP) in rats. The TMZ group did not show any statistically significant difference from the control group with respect to SEPs. However, the percentage of cells with ischaemic cell damage in hippocampal regions was significantly smaller in the TMZ group than the control group. Trimetazidine reduced the number of damaged cells in the cerebral tissue during the ischaemia-reperfusion damage. It was suggested that higher doses of trimetazidine may further reduce the number of cells with ischaemic damage.

Changes of somatosensory evoked potentials during writing with the dominant and non-dominant hands

Since close attention and special effort are necessary to perform difficult unskilled movements, particular brain activities underlying such movements could be expected to take place in the primary sensori-motor cortices (SI and MI). In this study we focused on such activities by analyzing the difference in the somatosensory evoked potential (SEP) in presence to the electrical stimulation of the median nerve during writing using the dominant and non-dominant hands in twelve right-handed and eight left-handed normal subjects. By alternately stimulating the right and left median nerves during the writing with either hand, SEPs were recorded from both hemispheres. During the dominant hand writing, the middle latency SEP components, i.e., parietal P25 and N33 and frontal N30, were significantly attenuated only in the hemisphere contralateral to the writing hand, corresponding to the conventional gating effect. During the non-dominant hand writing, not only those components recorded from the hemisphere contralateral to the writing hand, but also those from the hemisphere ipsilateral to the writing hand were significantly attenuated. In addition, N20 in the hemisphere contralateral to the writing hand was also significantly attenuated. There was no significant difference in the attenuation between the right-handed and left-handed subjects. The results indicated that the specific interaction between the signals after electrical stimulation and the sensory cortical activities related to the writing using the non-dominant hand occurred in both hemispheres, while it was recognized only in the hemisphere contralateral to the writing hand during the dominant hand writing. We speculate that the somatosensory cortex was more activated and thus interacted with the applied stimulation during the unskilled movement of the non-dominant hand compared to the movement of the dominant hand.

The AEP T-complex to synthesised musical tones: left-right asymmetry in relation to handedness and hemisphere dominance

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory 'musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and 'musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.

Inverse relationship between the size of pattern reversal visual evoked potentials from the left brain and the degree of left-hand preference in left-handed normal subjects: importance of the left brain

The relation of the degree of left-hand preference to pattern reversal visual evoked potentials (VEPs) from right and left brain was studied in male left-handers. The degree of the left-hand preference was assessed by the Waterloo Handedness Questionnaire. Visual stimuli consisted of black and white checkerboard patterns generated on a TV screen. VEPs were simultaneously recorded from occipital leads of the right and left hemispheres. The degree of left-hand preference was found to be inversely and significantly related to size of VEPs only from left brain, not from right brain. That is, the conduction time, amplitude, duration, and area of N1-P1 waves linearly decreased as the degree of left-hand preference increased. These results were in accord with the testosterone hypothesis of cerebral lateralization, but not compatible with the right shift theory of handedness. It was concluded that visuomotor control by the left brain would be the main biological correlate of left-hand preference with regard to sensorimotor and cognitive functions.

Distribution of paw preference in mongrel and tortoise-shell cats and the relation of hemispheric weight to paw preference: sexual dimorphism in paw use and its relation to hemispheric weight

The distribution of the right minus left (R - L) paw use and its relation to hemispheric weight was studied in tortoise-shell cats. Paw preference was assessed by a food reaching test. All males (N = 9) were left-preferent; females (N = 13) were predominantly right-preferent. There was an inverse relationship between the degree of left-paw preference and the right-brain weight in males (no correlation with left-brain weight). In females, the R - L paw use showed a negative linear correlation with the right- and left-brain weights: the right-pawedness decreased and the left-pawedness increased as the right- and left-brain weights increased. The distributions of the R - L paw use as well as the relationships between brain-weight and pawedness exhibited sexual dimorphism. The results suggest that mainly the genetic and hormonal factors may play an important role in emergence of motor asymmetry in cats. Annett's right shift theory of handedness was also discussed in light of these results.

The relation of hand preference to hand performance in left-handers: importance of the left brain

The associations among hand preference, hand skill (peg moving time, PMT) and hand performance (dot filling/20 s) were analyzed in left-handed subjects. In the total sample, the degree of left-hand preference linearly decreased from -100 to zero (Geschwind scores, GSs) as the number of dots placed by the right hand increased (direct correlation); the left hand did not show any significant relation to GSs. The right-hand PMT linearly decreased as the GSs decreased (negative linear correlation); the left hand skill did not exhibit any significant correlation with GSs. There was a negative linear correlation between right-hand PMT and dot-filling with right hand; the left-hand PMT was not related to dot-filling with left hand. In males, the right-hand PMT showed a negative linear correlation with GSs; no significant correlation between PMT and GSs was found for the left hand. There was a negative linear correlation between right minus left (R - L) PMT and GSs. Dot-filling with right hand was found to be positively linearly correlated with GSs (no correlation for the left hand). The L - R dot-filling showed a negative linear correlation with GSs. PMT for the right hand exhibited a significant negative linear relation to dot-filling only with right hand. Sex and familial sinistrality caused minor changes in these relationships. It was concluded that the left brain would constitute the main factor determining the degree of left-handedness.

Right and left hand skill in relation to cerebral lateralization in right-handed male and female subjects: the prominent role of the right brain in right-handedness

The associations between right and left hand skills to cerebral motor lateralization were studied in right-handed subjects with (FS+) and without (FS-) familial sinistrality. Hand preference was assessed by Oldfield questionnaire and hand skill by the peg moving task. The mean peg moving times (PMTs) and their standard deviations (SDs) were calculated for each hand. There was a significant positive linear correlation between the mean right and left hand PMTs. In males, the mean difference between the left and right PMTs (L-R) showed a significant negative linear correlation with the mean right hand PMTs. There was no significant correlation between these parameters in females. The mean L-R PMTs were found to be positively linearly correlated with the mean left hand PMT in FS- males, FS- and FS+ females (no correlation in FS+ males). The results indicated the contribution of the mean left hand PMTs to L-R hand skill is much higher than that of the mean right hand PMTs. In males, there was no significant correlation between SDs of the mean right and left hand PMTs. In females, SD of the mean right hand PMT was found to be positively linearly related to SD of the left hand PMT. In males, L-R SDs were found to be negatively linearly related to SDs of the mean right hand PMTs and positively linearly related to the SDs of the mean left hand PMTs. In females, only the mean left hand PMT positively linearly correlated with L-R SDs. Here again, the left hand prominently influenced the L-R SDs. In males, SD for the mean right hand PMT showed no relation to right hand PMT. There was, however, a negative linear correlation between SD of the mean right hand PMT and the left hand PMT (no correlations in female). It was concluded that the left hand (right brain) would be of higher significance than the right hand (left brain) in determining the degree of the right-bias in hand skill and its stability in right-handers.

Testosterone and somatosensory evoked potentials from right and left posterior tibial nerves in right-handed young adults

The relationship between serum testosterone level and somatosensory evoked potentials (SEP) from right and left posterior tibial nerves (PTN) was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. The amplitudes of P39 and N49 components of the SEPs from the left and right hemispheres of men and only from the left hemisphere of women were found to be negatively linearly and significantly correlated with serum testosterone. There was no significant correlation between P58 and N76 components and serum testosterone in these subjects. The correlations were found to be more prominent for the left hemisphere than the right hemisphere. The data were also analyzed considering eye and foot preferences. It was concluded that testosterone could be associated with the development of the somatosensory system during adolescence.