- Email: [email protected]
Post-synaptic components of the trigeminal evoked potentials in man
$73 landic cortex of 21 patients evaluated for surgery of intractabk epilepsy. High amplitude cortical responses (8.6-85.7 pN) tc contralateral MNS were recorded in all cases. Ipsilateral MNS. however, elicited no response within 60 msec in 19 out of 21 patients. These results are in good agreement with previous studies of direct cortical recordings in humans (Giblin 1964, Goldring et al 1970, Papakostopoulos et al 1975) and animals (Marshall et al 1941). Two cases showed ipsilateral EPs that had a very localized distribution, showed no initial negativity and decreased markedly with sleep (awake/sleep ratio = 2.8 and 3.0). Contrarily the contralateral EPs had a widespread distribution with a prominent initial negativity and were unchanged with sleep. The ipsilateral EPs showed a maximum amplitude 1 2 cm distant from the maximum of the contralateral EPs, had a P2 latency 1.2-17.8 msec longer and a P2 amplitude (2.0-22.0 /~V) 1.1-7.7 times smaller than the contralateral EPs. Electrical stimulation of the subdural electrodes did not elicit ipsilateral paresthesias. This suggests that the ipsilateral EPs are an expression of unconscious sensory information like, for example, kinesthetic or position sense of the ipsilateral hand.
W18.07 S I N U S O I D A L D E C O M P O S I T I O N OF MEDIAN NERVE S H O R T LATENCY S O M A T O S E N S O R Y EVOKED POTENTIALS (SSEPs).
P.J. Maccabee, N.F. Hassan and R.Q. Cracco
W18.08 POST-SYNAPYIC C O M P O N E N T S OF THE TRIGEMINAL EVOKED POTENTIALS IN MAN.
M. Leandri, C. Parodi, J. Zattoni and E. Favale (Genova, Italy) In a previous paper on trigeminal evoked potentials (Leandri et al. Electroenceph. Clin. Neurophysiol. 1985 In press) we described three neurogenic, presynaptic components (WI, W2 and W3). The investigation was then limited to these potentials because the following ones could be contaminated by muscular reflex activity. To overcome this difficulty in the present study we performed recordings in patients undergoing general anesthesia and curarization for abdominal surgery. The infraorbital nerve was stimulated and scalp potentials were recorded from 9 leads referred to a common electrode on the neck. Seven waves with diffuse distribution were recorded: the very early WI, W2 and W3 were followed by four small well-defined deflections labelled P4, N5, P6 and N7 (according to their polarity and latency) whose post-synaptic nature was demonstrated by paired stimulation. Over the face projection area contralateral to the stimulus we recorded a further wave named NI0. It is proposed that N10 would represent the 'primary' cortical response and the preceding waves would be the reflection of subcortical events~ Also, in some cooperative awake volunteers we were able to record all the waves up to N7, whereas N I 0 was obscured by muscular activity.
(Brooklyn, NY, USA) Median nerve SSEPs recorded using a non-cephalic reference were obtained from 10 normal subjects. Each time domain recording was transformed to the frequency domain and displayed as power spectral density (PSD). An inverse transform from the frequency to time domain was performed on selected major spectral bands and regions, and compared with the original SSEP recording (Hassan et al 1985). Our data revealed the expected decomposition of the time domain recording into a sum of sinusoids of differing frequencies. The particular mix of such sinusoids depended upon the relatively unique frequency distribution observed in the PSD of each subject's SSEP. Recent scalp and depth recordings of median nerve SSEPs suggest that fast frequency components later than 15 msec arise rostral to the thalamus (Hashimoto et al 1984; Tsuji et al 1984). These components include P17-N18, PI9-N20 and P21-N23 and subsequent inconsistent wavelets (Maccabee, 1983). Theoretically, sinusoidal oscillators at different frequencies may reflect distinct cell populations discharging within the same macro-neuroanatomical structure (Basar, 1983). We postulate that some of the quasi-sinusoidal fast frequency components between 15 and 26 msec represent the sum of a few damped sinusoids generated repetitively, sequentially or simultaneously within 2 or 3 neuron intracortical circuits.
W18.09 SUBCORTICAL S O M A T O S E N S O R Y EVOKED POTENTIALS F O L L O W I N G STIMULATION OF THE FACE.
I~E. Posthumus Meyjes (Amsterdam, The Netherlands) In contrast to the general agreement about the cortical nature of the N14 component of the trigeminal sensory evoked potential (TSEP), there is still some uncertainty about the origin of components with shorter latencies as described by Drechsler in 1980 and Singh in 1982, the so-called N3-5/P9 complex. When recorded with the same montage as used in BAER examinations (Cz to A1 or A2), a very stable P5-N9 complex can be found provided that the stimulus to one side of the lower lip reaches an intensity of twitch level. This response is not abolished by anaesthetic block of the mandibular nerve. However, the response was absent in a case of transection of the facial nerve following removal of an acoustic neuroma, in a case of skull base fracture with facial palsy and in a case of bilateral brain-stem infarction with a lesion of the facial nuclei. Stimulation of the lower lip or the mental nerve at intensities below twitch level, gives rise to a much less stable response with peak latencies at N5 and P9. Therefore, it is still uncertain whether these early components arise in the Gasserian ganglion a n d / o r in the trigeminal brain-stem nuclei.
W18.07 S I N U S O I D A L D E C O M P O S I T I O N OF MEDIAN NERVE S H O R T LATENCY S O M A T O S E N S O R Y EVOKED POTENTIALS (SSEPs).
P.J. Maccabee, N.F. Hassan and R.Q. Cracco
W18.08 POST-SYNAPYIC C O M P O N E N T S OF THE TRIGEMINAL EVOKED POTENTIALS IN MAN.
M. Leandri, C. Parodi, J. Zattoni and E. Favale (Genova, Italy) In a previous paper on trigeminal evoked potentials (Leandri et al. Electroenceph. Clin. Neurophysiol. 1985 In press) we described three neurogenic, presynaptic components (WI, W2 and W3). The investigation was then limited to these potentials because the following ones could be contaminated by muscular reflex activity. To overcome this difficulty in the present study we performed recordings in patients undergoing general anesthesia and curarization for abdominal surgery. The infraorbital nerve was stimulated and scalp potentials were recorded from 9 leads referred to a common electrode on the neck. Seven waves with diffuse distribution were recorded: the very early WI, W2 and W3 were followed by four small well-defined deflections labelled P4, N5, P6 and N7 (according to their polarity and latency) whose post-synaptic nature was demonstrated by paired stimulation. Over the face projection area contralateral to the stimulus we recorded a further wave named NI0. It is proposed that N10 would represent the 'primary' cortical response and the preceding waves would be the reflection of subcortical events~ Also, in some cooperative awake volunteers we were able to record all the waves up to N7, whereas N I 0 was obscured by muscular activity.
(Brooklyn, NY, USA) Median nerve SSEPs recorded using a non-cephalic reference were obtained from 10 normal subjects. Each time domain recording was transformed to the frequency domain and displayed as power spectral density (PSD). An inverse transform from the frequency to time domain was performed on selected major spectral bands and regions, and compared with the original SSEP recording (Hassan et al 1985). Our data revealed the expected decomposition of the time domain recording into a sum of sinusoids of differing frequencies. The particular mix of such sinusoids depended upon the relatively unique frequency distribution observed in the PSD of each subject's SSEP. Recent scalp and depth recordings of median nerve SSEPs suggest that fast frequency components later than 15 msec arise rostral to the thalamus (Hashimoto et al 1984; Tsuji et al 1984). These components include P17-N18, PI9-N20 and P21-N23 and subsequent inconsistent wavelets (Maccabee, 1983). Theoretically, sinusoidal oscillators at different frequencies may reflect distinct cell populations discharging within the same macro-neuroanatomical structure (Basar, 1983). We postulate that some of the quasi-sinusoidal fast frequency components between 15 and 26 msec represent the sum of a few damped sinusoids generated repetitively, sequentially or simultaneously within 2 or 3 neuron intracortical circuits.
W18.09 SUBCORTICAL S O M A T O S E N S O R Y EVOKED POTENTIALS F O L L O W I N G STIMULATION OF THE FACE.
I~E. Posthumus Meyjes (Amsterdam, The Netherlands) In contrast to the general agreement about the cortical nature of the N14 component of the trigeminal sensory evoked potential (TSEP), there is still some uncertainty about the origin of components with shorter latencies as described by Drechsler in 1980 and Singh in 1982, the so-called N3-5/P9 complex. When recorded with the same montage as used in BAER examinations (Cz to A1 or A2), a very stable P5-N9 complex can be found provided that the stimulus to one side of the lower lip reaches an intensity of twitch level. This response is not abolished by anaesthetic block of the mandibular nerve. However, the response was absent in a case of transection of the facial nerve following removal of an acoustic neuroma, in a case of skull base fracture with facial palsy and in a case of bilateral brain-stem infarction with a lesion of the facial nuclei. Stimulation of the lower lip or the mental nerve at intensities below twitch level, gives rise to a much less stable response with peak latencies at N5 and P9. Therefore, it is still uncertain whether these early components arise in the Gasserian ganglion a n d / o r in the trigeminal brain-stem nuclei.