Evaluation of breast sensibility using dermatomal somatosensory evoked potentials

This study was undertaken to prospectively evaluate breast sensibility before and after reduction mammaplasty with a new, objective, and quantitative neurophysiologic method based on the anatomic knowledge of breast innervation and the congruent areas of dermatomal maps. An innovative application of dermatomal somatosensory evoked potentials was used to study the breast regions of 42 healthy women, bilaterally. The areas stimulated in each breast were the superior quadrant, the nipple-areola complex and the medial and lateral quadrants, and the inferior quadrant; these areas correspond to T3, T4, and T5 dermatomes, respectively, following the accepted concepts of segmentary innervation of the skin. The two groups of 21 patients each were formed according to breast size: group I comprised small-breasted, unoperated controls (brassiere cup size A or B); group II comprised macromastia patients (brassiere cup size C or greater) who presented to a general plastic surgery department for breast reduction surgery. First the authors established the normal range of latency and amplitude in the dermatomal somatosensory evoked potentials for the five areas stimulated in patients with small breasts and compared these parameters with those obtained from patients with macromastia. Then, after the macromastia patients underwent reduction mammaplasty using the McKissock technique, the authors compared the postoperative sensory values with their own preoperative values and with those from the small-breasted group. Using dermatomal somatosensory evoked potentials, they found that small breasts were statistically more sensitive than large breasts, which concurs with studies in the literature that use other methods to evaluate breast sensibility. They also found that after breast reduction, the macromastia patients presented statistically significant improvement in breast sensibility in relation to their own preoperative latency and amplitude values, with no statistical difference in amplitude with respect to the small-breasted group; this finding suggests that after breast reduction, sensibility similar to that of the small-breasted group can be considered a possibility. Furthermore, in comparisons of each of the five areas stimulated, there was no significant difference in values within the small-breasted group or within the macromastia group before or after surgery; this supports a possible overlap between adjacent dermatomes. This innovative application of dermatomal somatosensory evoked potentials is an objective, quantitative, and noninvasive method that has allowed the authors to evaluate breast sensibility and to compare postsurgical sensory outcomes.     

Steady-state analysis of somatosensory evoked potentials

We report the development of a new method for frequency domain analysis of steady-state somatosensory evoked potentials (SEPs) to amplitude-modulated electrical stimulation, which can be recorded in significantly less time than traditional SEPs. Resampling techniques were used to compare the steady-state SEP to traditional SEP recordings, which are based on signal averaging in the time domain of cortical responses to repetitive transient stimulation and take 1–2 min or more to obtain a satisfactory signal/noise ratio. Median nerves of 3 subjects were stimulated continuously with electrical alternating current at several modulation frequencies from 7 to 41 Hz. Amplitude modulation was used to concentrate the power in higher frequencies, away from the modulation frequency, to reduce the amount of stimulus artifact recorded. Data were tested for signal detectability in the frequency domain using the T_circ² statistic. A reliable steady-state response can be recorded from scalp electrodes overlying somatosensory cortex in only a few seconds. In contrast, no signal was statistically discriminable from noise in the transient SEP from as much as 20 s of data. This dramatic time savings accompanying steady-state somatosensory stimulation may prove useful for monitoring in the operating room or intensive care unit.     

Auditory evoked potentials in distinguishing between peripheral and central tinnitus

Brainstem evoked response audiometry has been performed in 164 patients complaining of tinnitus, unilateral or bilateral. The latency of every wave and the latency between the peak of every wave have been compared with those obtained in a normal population (n = 57). The latency of the first wave is increased significantly at the same side of the tinnitus. But I-V latency is shorter at the side of the tinnitus. When this increase is absent, the I-V latency is prolonged the side of the tinnitus. It is possible to differentiate between tinnitus of peripheral origin and that of central origin, although the existence of unilateral deafness is constant. The same results have been obtained in the deaf patients with bilateral symmetric deafness, in accordance with Maurizi et al., 1985.     

痛觉诱发电位的研究进展

痛觉诱发电位的研究在过去的几十年内取得了重要进展 ,出现了许多用于被试的诱发明确疼痛感的刺激技术 ,并与诱发电位方法学联合应用 ,已经成为脑映像学研究中重要的组成部分。本文从刺激技术、痛觉诱发电位成分分析和偶极子源分析等方面出发 ,讨论了痛觉诱发电位的研究进展     

Temperature-dependent hysteresis in somatosensory and auditory evoked potentials

Fourteen adult patients undergoing open heart surgery under induced hypothermia had median nerve, short-latency somatosensory evoked potentials (SSEPs) recorded during cooling (from 36°C to 19°C) and subsequent rewarming. Similar data on another group of patients who had brain-stem auditory evoked potentials (BAEPs) were also analyzed. Hypothermia produced increased latencies of the major SSEP and BAEP components and the latencies returned to normal with subsequent warming. The temperature-latency relationship during the cooling phase was significantly different from that during the warming phase. For SSEP components the temperature-latency relationship was linear during cooling and curvilinear during warming, whereas for BAEP it was curvilinear both during cooling and warming. Furthermore, the regression curves were different during the two phases of temperature manipulation, particularly for temperatures below 30°C both for SSEP and BAEP components. At the onset of warming there was an initial exaggerated warming response on the evoked potential (EP) latencies and amplitude of the EP components. The temperature-latency regression curves were uniformly less steep during the warming phase compared to those during cooling. These findings suggest the existence of hysteresis in the relationship between temperature and EP latencies. The latencies at a given temperature below 30°C depend on whether that temperature is reached during cooling or during warming.     

Method for single-trial recordings of somatosensory evoked potentials

Evoked potentials (EPs) in response to stimuli are recorded from a human scalp contaminated with noise. To improve the signal-to-noise ratio, averaging methods have been widely used for the recorded data. However, when the waveforms of EP for each stimulus are not identical, the average waveform of the EP deteriorates. Variation of the EP waveform to each stimulus itself is important information for the EP. In this paper, a recording method for single somatosensory evoked potential (SEP) waveform is proposed, in which three kinds of band-pass filters were selectively used during three specific time sectors for each interstimulus interval. For the late section of the interval, an EEG waveform prediction method was applied to eliminate contaminated alpha rhythm components. By using the proposed method, we were successful in detecting the single SEP waveform.     

Somatosensory evoked potentials from the thalamic sensory relay nucleus (VPL) in humans: correlations with short latency somatosensory evoked potentials recorded at the scalp

Somatosensory evoked potentials (SEPs) were recorded in humans from an electrode array which was implanted so that at least two electrodes were placed within the nucleus ventralis posterolateralis (VPL) of the thalamus and/or the medial lemniscus (ML) of the midbrain for therapeutic purposes. Several brief positive deflections (e.g., P11, P13, P14, P15, P16) followed by a slow negative component were recorded from the VPL. The sources of these components were differentiated on the basis of their latency, spatial gradient, and correlation with the sensory experience induced by the stimulation of each recording site. The results indicated that SEPs recorded from the VPL included activity volume-conducted from below the ML (P11), activity in ML fibers running through and terminating within the VPL (P13 and P14), activity in thalamocortical radiations originating in and running througn the VPL (P15, P16 and following positive components) and postsynaptic local activity (the negative component). The sources of the scalp-recorded SEPs were also analyzed on the basis of the timing and spatial gradients of these components. The results suggested that the scalp P11 was a potential volume-conducted from below the ML, the scalp P13 and P14 were potentials reflecting the activity of ML fibers, the small notches on the ascending slope on N16 may potentially reflect the activity of thalamocortical radiations, and N16 may reflect the sum of local postsynaptic activity occurring in broad areas of the brain-stem and thalamus.     

Effect of body and foot positions on the somatosensory evoked potentials

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during sitting and standing with variable foot positions. During standing a decrease in the amplitude of the early positive component was observed. The deviation of the foot from a horizontal position was associated with an increase in the amplitude of the early negative component. The combined influence of body and foot positions showed a decrease in the amplitude of both early and late components. The standing position induced changes in more components than the varied foot positions. This suggests that maintenance of the standing posture is a more complex task than the maintenance of the foot position itself.     

Stimulus frequency dependence of the central and peripheral somatosensory evoked activity in rats treated with various pesticides

Rats were treated with a combination of insecticide agents in different timing schemes. In acute administration, 1/5 LD50 of the three insecticides: dimethoate, propoxur and cypermethrin, or their combination, was given once by gavage. In the developmental model, female rats received oral doses of 1/25 LD50 of the above insecticides in combination in three timing schemes including pregnancy and lactation. Responses in the somatosensory cortex and in the tail nerve, evoked by peripheral electric stimulation, were recorded in acute preparation under urethane anesthesia. It was tested whether the parameters of the cortical and peripheral evoked response are dependent on the frequency and whether this dependence is different in control and treated animals. The latency increase of the cortical responses with increasing stimulation frequency was significantly stronger in rats treated acutely with cypermethrin and the combination, and in rats receiving the combination during both intra- and extrauterine development. On the duration, the effects were less clear. Frequency dependent increase of the tail nerve action potential latency was significantly intensified by cypermethrin, and the amplitude decrease, by cypermethrin and dimethoate. Fatigue of this response during a stimulation series was also altered by the insecticides. Frequency dependence and fatigue possibly reflect the actual state of the nervous system and may have the potency to be developed to functional biomarkers.     

Origin and distribution of brain-stem somatosensory evoked potentials in humans

The distribution of somatosensory evoked potentials (SEPs) recorded from the brain-stem surface was studied to investigate their generator sources in 14 patients during surgical exploration of the posterior fossa. Two distinct SEPs of different morphologies and electrical orientation were obtained by median nerve stimulation. A small positive-large negative-late prolonged positive wave was recorded from the cuneate nucleus and its vicinity. There was a phase-reversal between the cuneate nucleus and the ventral surface of the medulla, depicting a dipole for dorso-ventral organization. From the pons and midbrain, triphasic waves with predominant negativity were obtained. This type of SEP had identical wave forms between dorsal, lateral and ventral surface of the pons and midbrain. It showed an increase in negative peak latency as the recording sites moved rostrally, suggesting an ascending axial orientation. In a patient with pontine hemorrhage, the killed end potential, a large monophasic positive potential was obtained from the lesion. This potential occurs when an impulse approaches but never passes beyond the recording electrode. Therefore, the triphasic SEP from the pons and midbrain reflects an axonal potential generated in the medial lemniscal pathway.     

Time-frequency component analysis of somatosensory evoked potentials in rats

Background  

Somatosensory evoked potential (SEP) signal usually contains a set of detailed temporal components measured and identified in a time domain, giving meaningful information on physiological mechanisms of the nervous system. The purpose of this study is to measure and identify detailed time-frequency components in normal SEP using time-frequency analysis (TFA) methods and to obtain their distribution pattern in the time-frequency domain.     

Development of cortical somatosensory evoked potentials in rats.

The development of the contra- and ipsilateral cortical potential evoked by electrical sciatic nerve stimulation was studied in 77 male albino rats aged 5 to 45 days. A contralateral response was already recorded, as double negativity, in the youngest animals, while an ipsilateral evoked potential was not reliably present until the 10th day. At this time, however, both responses started with an inconstant positive wave and their shape was practically the same. During subsequent development the responses differed only in respect to their dominant component: in the contralateral response, the N1 wave had the highest amplitude for most of the time, while in the ipsilateral response the delayed N2 wave was the largest component. The latent periods of contralateral responses were somewhat shorter than those of ipsilateral evoked potentials. During development we noticed a phase of abrupt shortening of the latent period, which took place before the 15th day in the contralateral response and before the 20th day in the ipsilateral response. We also found a difference in the fatigability of the responses, which was greater in immature rats than in adult animals; in the ipsilateral evoked potential it approached adult values more slowly. The development of the ipsilateral response is thus delayed compared with the development of the contralateral response.     

Abnormalities of short-latency somatosensory evoked potentials in parkinsonian patients

Twenty-two patients (16 affected by parkinsonian syndromes, 6 by other neurological diseases) and 12 age-matched controls were examined. Short-latency somatosensory evoked potentials were recorded from 30 scalp electrodes in the 45–52 msec following separate left and right median nerve stimulation at the wrist. Bit-colour maps were generated on a 4096 pixel matrix via quadratic interpolation. Peak latencies and amplitudes of the parietal, central and frontal components were evaluated. Moreover, the amplitude ratios between parietal and frontal components on the same hemiscalp and between peaks on homologous right and left scalp districts were taken into account. The unique significant difference between parkinsonians and controls was represented by a depressed frontal N₃₀ wave. This peak was absent in 3 and reduced in 7 out of 16 parkinsonians, with an overall abnormality rate of 47% of the examined arms. Average maps pooling data of parkinsonians and controls confirmed the presence of reduced evoked activity for the whole duration of wave N₃₀ on those mid- and parasgittal frontal districts where this peak is maximally represented in normals. A similar abnormality was found in 1 of the 6 non-parkinsonian neurological patients suffering from a meningioma of the falx compressing the left supplementary motor area. Possible pathophysiology of such wave N₃₀ abnormalities in parkinsonians is discussed.     

The interaction of the somatosensory evoked potentials to simultaneous finger stimuli in the human central nervous system. A study using direct recordings

In order to investigate the interaction of sensory electrophysiologic fields arising from the adjacent second (II) and third (III) fingers and the distant second and fifth (V) fingers, direct recordings of somatosensory evoked potentials (SEPs) were performed from the sensory and motor cortices, the sensory thalamic nucleus (nucleus ventralis caudalis, VC) and the cuneate nucleus in humans during neurosurgical operations. Electrical stimulation was given to the II, III or V fingers individually, and also to pairs of either the II and III fingers or the II and V fingers simultaneously. The interaction ratio OR) was devised as the ratio of amplitude attenuation caused by the simultaneous stimulation to two fingers compared with the amplitude of the arithmetically summed SEPs to the individual stimulation of two fingers. The IRs were calculated on N20 and P25 from the sensory cortex, P22 from the motor cortex, P17_thal from the VC, and N16_cune and P35_cune from the cuneate nucleus.With both stimulations to the II and III fingers and the II and V fingers, P25 showed the greatest IR, followed by P22, then by P17_thal while N16_cune exhibited the smallest IR. N20 and P35_cune showed similar IRs and significantly greater IRs with II and III finger stimulation compared with II and V finger stimulation.These results thus indicate that the interaction of somatosensory impulses occurs in several structures along the sensory pathway in CNS, including the cuneate nucleus, the sensory thalamic nucleus, as well as sensory and motor cortices, with the greatest IRs in the cerebral cortices and the weakest ones in the brain-stem. They also suggest that the receptive fields of the fingers in the cortical area generating N20 are arranged according to the order of the fingers while those in the generating sites for cortical P25 and P22, thalamic P17_thal and cuneate N16_cune tend to be arranged in clusters, while P35_cune is possibly modulated by the somatosensory cortex through a long-loop feedback pathway.     

Scalp topography of mechanically and electrically evoked somatosensory potentials in man

Scalp topography of somatosensory evoked potentials following mechanical (SEPs(M)) and electrical (SEPs(E)) stimulation of the left middle finger was investigated with linked ear reference in 21 normal young adults. A small plastic ball (touch) or needle (pain) was used for the mechanical stimulation. With mechanical stimulation, at least 3 positive and 3 negative potentials (P19(M), N24(M), P29(M), N36(M), P49(M) and N61(M)) were found in the post-rolandic area contralateral to the stimulation. The wave form in SEPs(M) was similar to those in SEPs(E), but the peak latency of each component in SEPs(M) was 1–4 msec longer than that in SEPs(E). Earlier components such as P19(M), N24(M) and P29(M) were not as clearly recognized as corresponding components in SEPs(E). However, the wave form recorded on the hemisphere ipsilateral to the stimulation or in the frontal area contralateral to the stimulation showed a greater difference from subject to subject. P19(M), N24(M) and P29(M) correlated positively both with arm length and height of the subject. There was no significant difference of the wave form between the linked ear reference and the bipolar (C4-Fz) derivation. Wave form of SEPs(M) by needle stimulation did not significantly differ from that by plastic ball stimulation.