Higher-order non-linear phenomena in Renshaw cell responses to random motor axon stimulation (original) (raw)
Neuroscience, 1989
Lumbosacral Renshaw cells were activated by random stimulation of motor axons in muscle nerves or ventral roots. The stimulus patterns had mean rates of 9.5-13 or 2&23 pulses per second. The Renshaw cell responses were evaluated by two kinds of ~ristimulus-time histograms. "Conventional" peristimulus-time histograms were calculated by averaging the cell discharge with respect to all the stimuli in a train, "Conditional" peristimulus-time histograms were determined by averaging the cell discharge with respect to the second ("test") stimulus in pairs of stimuli which were separated by varied intervals. The effects of the conditioning stimuli were evaluated after correcting for the effect of linear superposition of the conditioning and test stimuli.
Neuroscience, 1989
spinal Renshaw cells were activated by stimulating muscle nerves or ventral roots with random (pseudo-Poisson) patterns of brief electrical stimuli. This input pattern is optimal for a comparative study in both the frequency-and time-domain. The frequency-dependent variable of particular interest in this study was the coherence as a measure of the degree to which signal transmission is linear and noise-free; it was estimated via spectral analysis. Time-domain analysis consisted of calculating ~~-stimulus time histograms in order to estimate the amount of nonlinea~ty in the cell responses to pairs of stimuli. The main result was that the amount of nonlinearity measured in this way did not profoundly depress the coherence.
Experimental Brain Research, 1988
In 9 adult anaesthetized cats, 22 lumbosacral Renshaw cells recorded with NaCl-filled micropipettes were activated by random stimulation of ventral roots or peripheral nerves. The stimulus patterns had mean rates of 9.5~13 or 20–23 or 45 pulses per second and were pseudo-Poisson; short intervals below ca. 5 ms (except in two cases) were excluded. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms (PSTHs). “Conventional” PSTHs were calculated by averaging the Renshaw cell discharge with respect to all the stimuli in a train. These PSTHs showed an early excitatory response which was often followed by a longer-lasting slight reduction of the discharge probability. These two response components were positively correlated. “Conditional” PSTHs were determined by averaging the Renshaw cell discharge with respect to the second (“test” stimulus in pairs of stimuli which were separated by varied intervals, δ. The direct effect of the first “conditional” response was subtracted from the excitation following the second (“test” stimulus so as to isolate the effect caused by the second stimulus per se. After such a correction, the effect of the first “conditioning” stimulus showed pure depression, pure facilitation or mixed facilitation/depression. Analysis of such conditioning curves yielded two time constants of facilitation (ranges: ca. 4–35 ms and 93–102 ms) and two of depression (ranges: ca. 7–25 ms and 50–161 ms). It is concluded that these time constants are compatible with processes of short-term synaptic plasticity known from other synapses. Other processes such as afterhyperpolarization and mutual inhibition probably are of less importance.
In 9 adult anaesthetized cats, 22 lumbosacral Renshaw cells recorded with NaCl-filled micropipettes were activated by random stimulation of ventral roots or peripheral nerves. The stimulus patterns had mean rates of 9.5-13 or 20-23 or 45 pulses per second and were pseudo-Poisson; short intervals below ca. 5 ms (except in two cases) were excluded. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms (PSTHs). "Conventional" PSTHs were calculated by averaging the Renshaw cell discharge with respect to all the stimuli in a train. These PSTHs showed an early excitatory response which was often followed by a longer-lasting slight reduction of the discharge probability. These two response components were positively correlated. "Conditional" PSTHs were determined by averaging the Renshaw cell discharge with respect to the second ("test") stimulus in pairs of stimuli which were separated by varied intervals, 6. The direct effect of the first "conditional" response was subtracted from the excitation following the second ("test") stimulus so as to isolate the effect caused by the second stimulus per se. After such a correction, the effect of the first "conditioning" stimulus showed pure depression, pure facilitation or mixed facilitation/depression. Analysis of such conditioning curves yielded two time constants of facilitation (ranges: ca. 435 ms and 93-102 ms) and two of depression (ranges: ca. 7-25 ms and 50-161 ms). It is concluded that these time constants are compatible with processes of short-term synaptic plasticity known from other synapses. Other processes such as afterhyperpolarization and mutual inhibition probably are of less importance.
Factors affecting modulation in post-stimulus histograms on static fusimotor stimulation
Brain Research, 1977
Stimulation of static fusimotor axons commonly produces a pulsatile excitatory effect on the discharge of the Ia afferent from the primary ending of the muscle spindle. In the extreme, this manifests itself as 1:1 driving of the afferent by the motor stimulus. In other cases, the effect may be demonstrated by the occurrence of phase-locked modulation in the frequencygram 2 (i.e. superimposed records of instantaneous frequency) or in the post-stimulus time (PST) histogram ~,8,14. The effect appears attributable to the twitch properties of the nuclear chain fibres, and perhaps also of the bag2 fibres. However, such phased modulation is not normally seen on stimulation of dynamic axons 2,s, presumably because these act almost exclusively through the apparently non-twitching bagl fibres, Certain evidence 1,7 favours the view that static axons sometimes also supply the bagl fibres and that their contraction may then influence the response of the primary ending to stretching applied during static fusimotor stimulation, although having little effect with the muscle at constant length. Any such contribution from bagl activation during static action should be unaccompanied by driving tendencies, and might even interfere with them. This has led us to compare PST histograms obtained when the muscle length was held constant with those obtained while it was being lengthened or shortened at constant velocity during 'triangular stretching', since different contributions might then be expected from the terminals on the three types of intrafusal fibre to the overall response of the primary afferent. The experiment is also of special interest in relation to hypotheses that the la afferent possesses more than one site of impulse initiation (pacemaker) and that dominant activity may switch between them under different conditions 4,6,12,13. Changes in modulation might provide a sign of switching between, for instance, bag1 and chain pacemakers.
Journal of Integrative Neuroscience, 2004
We employ computer simulations to explore the effect of different temporal patterns of afferent impulses on the evoked discharge of a model cerebellar Purkinje cell. We show that the frequency and temporal correlation of impulses across afferent fibers determines which of four regimes of discharge activity is evoked. In the uncorrelated, here Poissonian, case, (i) cell discharge is determined by the total stimulation rate and temporal patterns of discharge are the same for different combinations of afferent fiber number and mean impulse rate per fiber giving the same total stimulation. Alternatively, if temporal correlations are present in the stimulus, (ii) for stimulation frequencies of 4 to at least 64 Hz there is a narrow range of afferent fiber number for which every stimulus pulse (composed of a single impulse on each afferent fiber) evokes a single action potential. In this case cell discharge is frequency locked to the stimulus with a concomitant reduction in discharge variability. (iii) For lower fiber numbers and thus discharge frequencies lower than the locking frequency, the variability of cell discharge is typically independent of afferent impulse timing, whereas, (iv) at higher fiber numbers and thus higher discharge frequencies, the reverse is true. We conclude that in case (iii) the cell acts as an integrator and discharge is determined by the stimulation rate, whereas in case (iv) the cell acts as a coincidence detector and the timing of discharge is determined by the temporal pattern of afferent stimulation. We discuss our results in terms of their significance for neuronal activity at the network level and suggest that the reported effects of varying stimulus timing and afferent convergence can be expected to obtain also with other principal cell types within the central nervous system.
Spinal Source for the Synchronous Fluctuations of Bilateral Monosynaptic Reflexes in Cats
Journal of Neurophysiology, 2005
Successive stimuli of constant intensity applied to Ia afferents produce spinal monosynaptic reflexes (MSRs) of variable amplitude. We recorded simultaneous MSRs in the left and right L7 (or L6) ventral roots of anesthetized cats. We analyzed the cross-covariance (CCV) between the amplitudes of bilateral MSRs. Long-time series (5 to 8 h) of these bilateral MSRs exhibited transitory changes in their covariations (as measured by the zero-lag peak of their CCV), thus suggesting the existence of certain neural sources contributing to produce these changes. The aim of the present study was to show that spinal centers producing negative spontaneous cord dorsum potentials (nSCDPs) contribute to maintain correlations in the amplitude of bilateral MSRs. After spinal cord transection at the L1 segment, no significant changes were observed in the correlation between the amplitude of bilateral nSCDPs versus the amplitude of bilateral MSRs. However, this correlation, as well as the peak at zero ...
Effects of a photic input on the human cortico-motoneuron connection
Clinical Neurophysiology, 2000
Objectives: Disease manifestations such as photic cortical re¯ex myoclonus or myoclonus due to intermittent light stimulation rely on a pathologic interaction between non-structured visual inputs and the corticospinal system. We wanted to assess the normal interaction, if any, between a prior photic input and the output of the cortico-motoneuron connection. Methods: In 9 consenting healthy subjects we quanti®ed the changes exerted by a sudden, unexpected bright light¯ash on (i) the motor potentials (MEPs) evoked in the right ®rst dorsal interosseous muscle (FDI) by transcranial magnetic or electrical stimulation (TMS/TES) of the primary motor cortex, (ii) the FDI F-waves and (iii) the soleus H-wave. Separately, we measured the simple reaction times to the¯ash itself. All determinations were repeated twice with an interval of 2±24 months. Results: When the¯ash preceded TMS by 55±70 ms, the MEP size was reduced, while at interstimulus intervals (ISIs) of 90±130 ms it was enlarged. Statistical signi®cance (P , 0:05) emerged at ISIs of 55, 70, 100, 105 and 120 ms. Conversely, the MEP latency was prolonged at ISIs of 55±70 ms and shortened at ISIs of 90±130 ms (P , 0:05 at ISIs of 55, 110 and 130 ms). Electrical MEPs were enhanced at an ISI of 120 ms. The F-wave size showed a non-signi®cant trend of enhancement at ISIs of 90±130 ms. The soleus H-wave showed signi®cant enlargement at ISIs of 90±130 ms (P , 0:05 at ISIs of 100 and 105 ms). The minimum reaction time was on average 120 ms. Conclusions: An unexpected photic input, to which no reaction is planned, can cause an early inhibition of the responses to TMS. We think its origin lies within the primary motor cortex, since it is not associated with changes in spinal excitability or electrical MEPs. A later facilitation persists using TES and has a temporal relationship with an enlargement of the soleus H-wave. Thus, it likely results from activation of descending (possibly reticulospinal) ®bers that excite the spinal motor nucleus.