11 research outputs found

    Post-spike facilitation of neck EMG by cat tectoreticulospinal neurones during orienting movements.

    No full text
    1. The activity of fourteen tectoreticulospinal neurones (TRSNs) was recorded intraaxonally in the caudal pons of alert cats during orienting movements towards visual stimuli. TRSN spikes were used to compute the spike-triggered average (STA) of rectified EMG of dorsal neck muscles. 2. Eight TRSNs for which 400-2532 spikes were available were analysed with the STA technique. When the STA was computed from all spikes, significant post-spike facilitation (PSF) was obtained for six of eighteen cell-muscle pairs investigated (5 TRSNs). The mean relative amplitude of PSFs was 7.4% (S.D. 3.7). The onset latencies ranged from 1.1 to 5.0 ms and mean duration was 11.4 +/- 3.1 ms (mean +/- S.D.). 3. Interspike interval distributions were unimodal, with modes between 2.7 and 12.7 ms. Spike trains of TRSNs that produced significant PSFs contained 5-13% of the interspike intervals < or = 5 ms and 22-37% of the intervals < or = 10 ms. To evaluate the contribution of short intervals to PSF, STAs were computed separately for spikes preceded by 'short' (< or = 5 or < or = 10 ms) and 'long' (> 5 or > 10 ms) intervals. 4. When computed from spikes preceded by 'long' intervals, PSF amplitudes were small (mean +/- S.D., 5.3 +/- 2.7%) and onset latencies measured by cusum ranged between 2.4 and 5.4 ms. This is longer than the estimated minimal latency of monosynaptic facilitatory effect on neck EMG (1.9-2.1 ms). 5. Relative amplitudes of PSF obtained with spikes preceded by 'short' intervals were much larger (mean +/- S.D., 14.8 +/- 7.4%), but cusums indicated negative latencies for four of six PSFs. The unrealistically short onset latencies could be accounted for by the summation of facilitation from the trigger spike with that of the preceding spikes. In four of five TRSNs a large increase of PSF amplitude (from 3.2 to 7.2 times the amplitude obtained from 'long' intervals) suggests the presence of frequency-dependent potentiation of synaptic transmission. 6. This study unequivocally demonstrates that some TRSNs produce significant post-spike facilitation of neck motoneurones. This facilitation could be mediated by monosynaptic tectomotoneuronal connections although a contribution by disynaptic connections cannot be definitively ruled out. The high instantaneous firing rates of TRSNs produce a potentiation of the otherwise weak facilitatory action of TRSNs that presumably contributes to a rapid recruitment of motoneurones during initiation of head orienting movements

    The control of slow orienting eye movements by tectoreticulospinal neurons in the cat: behavior, discharge patterns and underlying connections

    No full text
    The activity of tectoreticulospinal neurons (TRSN) during orienting gaze shifts was studied in alert, head-fixed cats by intra-axonal recordings. The scope of the study was to evaluate the role of this class of superior colliculus neurons in the generation of slow eye movements (drifts) which often follow main-sequence saccades and sometimes appear as an independent motor event of orienting. The parameters of such movements are described in the first part of the paper. The organization of underlying pathways in the lower brainstem has been studied by intra-axonal horseradish peroxidase (HRP) tracing. The mean amplitude of postsaccadic drifts (PSD) is 1.21 degrees (SD 0.63), but it can eventually reach 6-8 degrees. PSDs have mean velocity of 14.9 degrees/s (SD 4.28) and mean duration of 104.2 ms (SD 50.8). These two parameters are positively correlated with PSD amplitude. The presence of PSDs is usually associated with an increased neck muscle activity on the side toward which the eyes move. The durations of these two motor events show a reliable positive correlation. PSDs appear to occur when gaze error persists after a saccade and a correction is attempted by means of a slow eye movement and a head turn. The durations of TRSN bursts are, on average, longer than the sum of the lead time and the saccade duration. Bursts associated with combinations of saccades and PSD are significantly longer than those recorded in the absence of PSDs. The probability of occurrence of PSDs is higher when firing of TRSNs continues after saccade termination. Such prolonged discharges usually coincide with a combination of PSDs and phasic activation of the neck electromyogram. The mean firing rate of TRSNs during PSDs is 62% of that during saccade-related portions of the burst and declines to 45% after the end of PSDs. According to its timing and intensity, postsaccadic firing of TRSNs is appropriate as a signal underlying slow, corrective eye movements and later portions of phasic neck muscle contractions during orienting. Intra-axonal HRP labeling showed that visuomotor TRSNs of the X type (n = 3) terminate in the abducens nucleus, with 145-331 boutons terminaux and en passant. Average bouton densities in the nucleus are lower than in the periabducens reticular formation, but higher than in more rostral paramedian pontine reticular formation (PPRF) regions. Terminal fields in the PPRF match the locations of "eye-neck' reticulospinal neurons (RSNs) and exitatory burst neurons.(ABSTRACT TRUNCATED AT 400 WORDS

    Effect of gaze direction on neck muscle activity during cervical rotation

    No full text
    Control of the neck muscles is coordinated with the sensory organs of vision, hearing and balance. For instance, activity of splenius capitis (SC) is modified with gaze shift. This interaction between eye movement and neck muscle activity is likely to influence the control of neck movement. The aim of this study was to investigate the effect of eye position on neck muscle activity during cervical rotation. In eleven subjects we recorded electromyographic activity (EMG) of muscles that rotate the neck to the right [right obliquus capitis inferior (OI), multifides (MF), and SC, and left sternocleidomastoid (SCM)] with intramuscular or surface electrodes. In sitting, subjects rotated the neck in each direction to specific points in range that were held statically with gaze either fixed to a guide (at three different positions) that moved with the head to maintain a constant intra-orbit eye position or to a panel in front of the subject. Although right SC and left SCM EMG increased with rotation to the right, contrary to anatomical texts, OI EMG increased with both directions and MF EMG did not change from the activity recorded at rest. During neck rotation SCM and MF EMG was less when the eyes were maintained with a constant intra-orbit position that was opposite to the direction of rotation compared to trials in which the eyes were maintained in the same direction as the head movement. The inter-relationship between eye position and neck muscle activity may affect the control of neck posture and movement
    corecore