Changes in central delay of soleus H reflex after facilitatory or inhibitory conditioning in humans

1. Central delay (CD) changes after facilitatory or inhibitory conditioning of the soleus H reflex have been investigated in a group of normal subjects as a function of the conditioning and test stimulus intensities and also as a function of the Hmax/Mmax ratio. Both facilitation and inhibition of the reflex response have been obtained by conditioning stimulation of the ipsilateral tibial nerve at suitable conditioning-test stimulus intervals. CD changes have been extrapolated from the variations of the time interval between afferent and efferent neural volleys underlying the H reflex, directly recorded from the sciatic nerve. 2. The CD was significantly decreased by facilitatory and increased by inhibitory conditioning. Facilitatory CD changes were positively related to test stimulus strength (at a given conditioning stimulus intensity) and negatively related to conditioning stimulus strength (at a given test stimulus intensity). Both trends were reversed after inhibitory conditioning. The effectiveness of facilitatory conditioning was positively related to the individual Hmax/Mmax ratio whereas a negative relationship could be observed after inhibitory conditioning. 3. Also, the "conditioning threshold" (the minimal conditioning stimulus strength affecting the reflex size) and the "maximal conditioning effect" (the conditioning stimulus intensities leading to either the saturation of the facilitatory effect or the suppression of the reflex response) were significantly related to the Hmax/Mmax ratio. 4. We suggest that temporal changes in the H reflex pathway after facilitatory or inhibitory conditioning stimuli depend both on the size of the motoneuronal pool underlying the reflex response, as determined by the test stimulus intensity, and on the individual excitability of the motoneuronal pool, as defined by the Hmax/Mmax ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

F-wave and Cervical Somatosensory Response Conduction from the Seventh Cervical Spinous Process to Cortex in Multiple Sclerosis

SUMMARY:Transit (conduction) times from the wrist to the seventh cervical spinous process (C7) were measured by using the F-wave response (TA) and the cervical somatosensory response (SEPC). The mean values obtained in 25 controls were 10.1 ± 0.9 s-3 and 10.9 ± 1.0 s-3 respectively. The 0.8 ± 1.0 s-3 difference between the two methods represents central delay of SEPC, possibly at the level of the dorsal root ganglion. The mean onset latency of the cortical somatosensory response (SEPA) evoked by median nerve stimulation in the same subjects was 15.5 ± 1.0 s-3. Transit time from C7 to the cortex (TB) given by either SEPA - TA or SEPA - SEPC - 0.8, where 0.8 is the necessary corrective factor for central delay of SEPC, was 5.3 ± 1.0 s-3. These techniques were applied to 10 patients suspected of having multiple sclerosis, but without clinical evidence of involvement above C7. Six of the 10 cases showed prolongation of TB. In 4 of these, this could only be calculated by the F-wave method since SEPC was absent. It is concluded that transit times derived from either the F-wave or SEPC are equally valid and interchangeable. The absence of one response allows for its replacement by the other.

Parametric studies of dorsal horn neurons responding to tactile stimulation

Dorsal horn neurons responding to tactile input were recorded in segments L3-S2 of unanesthetized, low-spinal cats. Single units were characterized with regard to receptive field (RF) location, RF size and shape, spontaneous discharge rate, central delay, and convergence of four tactile afferent types. 1. RF size increased from the toes to the calf region. 2. Length-width ratio increased from the toes to the calf and declined from the calf to the hip. 3. The relation between RF size and position on the limb was independent of segmental and laminar location of the neurons. 4. RF size was positively correlated with spontaneous discharge rate. 5. The relation between RF size and shape and RF position can be interpreted in terms of regional variations in the magnitude of the gradient of representation in the dorsal horn somatotopic map. 6. Central delay was negatively correlated with both RF size and rate of ongoing discharge. 7. There were no statistically significant differences among the laminae with respect to central delay, RF size or shape, ongoing discharge, or convergence combinations of the four tactile afferent systems. 8. Data presented were at variance with Wall's laminar cascading model for laminae IV-VI. Our results suggest that the model should be modified, at least to emphasize monosynaptic tactile input to all three of these laminae.