Prestimulus Rate Research Articles

Spinal inhibition and motor function in adults with spastic cerebral palsy.

Abnormal activation of motoneurons in the spinal cord by sensory pathways is thought to contribute to impaired movement control and spasticity in individuals with cerebral palsy. Here we use single motor unit recordings to show how individual motoneurons in the spinal cord respond to sensory inputs in a group of participants with cerebral palsy having different degrees of motor dysfunction. In participants who had problems walking independently and required assistive devices such as wheelchairs, sensory pathways only excited motoneurons in the spinal cord. In contrast, in participants with cerebral palsy who walked independently for long distances, sensory inputs both inhibited and excited motoneurons in the spinal cord, similar to what we found in uninjured control participants. These findings demonstrate that in individuals with severe cerebral palsy, inhibitory control of motoneurons from sensory pathways is reduced and may contribute to motor dysfunction and spasticity. Reduced inhibition of spinal motoneurons by sensory pathways may contribute to heightened reflex activity, spasticity and impaired motor function in individuals with cerebral palsy (CP). To measure if the activation of inhibitory post-synaptic potentials (IPSPs) by sensory inputs is reduced in CP, the tonic discharge rate of single motor units from the soleus muscle was plotted time-locked to the occurrence of a sensory stimulation to produce peri-stimulus frequencygrams (PSFs). Stimulation to the medial arch of the foot was used to activate cutaneomuscular afferents in 17 adults with bilateral spastic CP and 15 neurologically intact (NI) peers. Evidence of IPSP activation from the PSF profiles, namely a marked pause or reduction in motor unit firing rates at the onset of the cutaneomuscular reflex, was found in all NI participants but in only half of participants with CP. In the other half of the participants with CP, stimulation of cutaneomuscular afferents produced a PSF profile indicative of a pure excitatory post-synaptic potential, with firing rates increasing above the mean pre-stimulus rate for 300ms or more. The amplitude of motoneuron inhibition during the period of IPSP activation, as measured from the surface EMG, was less in participants with poor motor function as evaluated with the Gross Motor Functional Classification System (r=0.72, P<0.001) and the Functional Mobility Scale (r=-0.82, P<0.001). These findings demonstrate that in individuals with CP, reduced activation of motoneuron IPSPs by sensory inputs is associated with reduced motor function and may contribute to enhanced reflexes and spasticity in CP.

China’s Fiscal Stimulus and the Recession Australia Never Had: Is a Growth Slowdown Now Inevitable?

China's timely and well-targeted two-year fiscal stimulus was particularly effective in stimulating growth in Australia's commodity exports. Using a constructed series of export volumes to China, this paper finds that the post-stimulus GDP growth contribution from export volumes to China is significant. Had growth in export volumes to China been commensurate with pre-stimulus rates, Australia would have experienced three consecutive quarters of negative real GDP growth - a technical recession. China's gradual and uniquely revenue-based unwinding of fiscal stimulus reduces the risk to Australia of an imminent growth slowdown.

A study of synaptic connection between low threshold afferent fibres in common peroneal nerve and motoneurones in human tibialis anterior

We have induced H-reflex responses in human tibialis anterior motor units and analysed the results using the classical technique, peristimulus time histogram (PSTH), and a new technique, peristimulus frequencygram (PSF). The PSF has recently been shown to be more reliable than the PSTH for indicating the synaptic connections on motoneurones, and therefore we wished to examine the differences between the two analysis methods. Experiments were conducted on eleven healthy subjects (7 males and 4 females) who did not have any known neurological disorder. The subject sat comfortably on a dental chair and the common peroneal nerve was stimulated. In each experiment, about 600 electrical stimuli were applied to the nerve randomly between 1 and 2 s. The recordings were taken with both by surface electromyogram (SEMG) and as single motor unit potentials. We found that, when a stimulus induces an H-reflex, it also generates a period of reduced activity (silent period) and a long latency excitation in the PSTH. However, the PSF records in general do not match the indications of the PSTH records. For example, when the PSTH indicated existence of a silent period immediately following the H-reflex response, the discharge rate of the unit was in fact higher than the prestimulus rate. On the contrary, during the PSTH illustrated long latency excitatory response, the discharge rate was lower than the prestimulus rate. Our findings suggest that PSF gives significantly different results compared with the PSTH in determining the synaptic connection of the low threshold muscle afferents to the motoneurones. While PSTH indicated that there was a silent period immediately after the H-reflex, the PSF demonstrated that the silent period was actually a continuation of the net excitatory effect and not a genuine inhibition since the small number of action potentials occured during this period displayed higher discharge rates than the prestimulus level. Furthermore, the long latency excitation, as it was indicated in the PSTH; was actually a net inhibitory effect since the large number of spikes that occured during that period had lower discharge rates than the prestimulus average. In the lights of the recent brain slice findings and completely different results obtained using the two analysis techniques, we suggest that the PSF analysis should be used along with the PSTH to illustrate the net synaptic connection between peripheral receptors and motoneurones in the human nervous system.

Male Calling Behavior and Female Choice in the Neotropical Treefrog Hyla microcephala

AbstractThe effect of stimulus call complexity and calling rate on the vocal responses of males and female mate choice was studied in Hyla microcephala in Panama. Males increased the number of notes in their calls in response to increases in stimulus call complexity during both playback of 1 to 8‐note advertisement calls and during natural interactions. However, precise matching of the number of notes in stimuli and responses did not occur consistently. Males also increased calling rates if stimuli were presented above prestimulus rates. Two‐stimulus choice experiments demonstrated that females prefer both higher calling rates and greater call complexity, indicating that the ways males change their vocal behavior during interactions increases their attractiveness to potential mates. Tests in which the relative intensity of a high and low rate stimulus was varied indicated that females prefer stimuli with higher total sound energy. In a natural chorus, it is likely that females simply approach males giving the most conspicuous calls.

Chlordiazepoxide and successive discrimination: Different effects on acquisition and performance

Benzodiazepines have been reported to increase low rates of responding during a stimulus correlated with non-reinforcement while leaving prestimulus rates unaffected (successive discrimination). However, the results have been obtained by superimposition of the drug upon a discrimination which was learned in the absence of drug. The observed effects may therefore have been due to the sudden change in drug state (state-dependency) rather than to a specific action of the drug. The present experiments found that chronic administration of chlordiazepoxide (5 mg/kg, IP) impaired acquisition but not performance of successive discrimination. Intermittent administration of chlordiazepoxide impaired discrimination by increasing low rates of responding during the stimulus signalling non-reinforcement. This effect was obtained with saline-drug but not drug-saline state changes (asymmetric state-dependency). A final experiment showed that chronic administration of the drug did reduce well-learned inhibition resulting from signalled shock. It was concluded that chlordiazepoxide has not only pure anxiolytic but also state-dependent dependent effects and that if successive discrimination depends on conditioned frustration it does so only while the discrimination is being learned.

Infant heart rate response to trigeminal airstream stimulation: determination of normal and deviant values.

In this study, trigeminal airstream stimulation is used on a group of normal, sleeping infants to screen for reflex bradycardia. Infants were tested at 1--3 days and at 4, 8, 12, and 16 weeks of age. The usual heart rate response was acceleration above the prestimulus level. The amount of heart rate change was seen to depend on prestimulus rate and, to a lesser extent, postconceptional age. Multiple regression analysis of the data provided estimates of expected responses, given postconceptional age and prestimulus heart rate. From these, ranges were established for classification of normal or abnormal responses. Six deviant data points over 2 SDs from expected values were identified. Two of these represented heart rate increases and four were heart rate decreases. One deviant heart rate decrease was over 3 SDs from the mean. Although the deviant increases were thought to represent exaggerated startles, the more severe heart rate decreases were believed to be a reflex resembling the diving reflex.

Thigmomorphogenesis: Electrical Resistance and Mechanical Correlates of the Early Events of Growth Retardation due to Mechanical Stimulation in Beans

The early effects of mechanical stimulation of stems have been examined in Phaseolus vulgaris. Auxanometry has revealed that within 3 minutes after stimulation, there is a brief but significant 33 % stimulation of growth which ceases by 6 minutes. After this, there is complete cessation of elongation which lasts from 15 to 30 minutes, after which growth resumes at a little more than half of the pre-stimulus rate. During the brief period of stimulated growth, the electrical resistance of the tissue decreases within seconds after stimulation. This effect can also be detected at the cut base of excised plants as a decrease of the resistance of the solution bathing them. The resistance of the stem tissue recovers during the period of zero growth. These and other data indicate that electrolyte efflux coupled with decreases in the electrical resistance of cell membranes, are among the very early events of thigmomorphogenesis.

Effects of hippocampal lesions on heart rate in aversive classical conditioning

Groups of hippocampal-lesioned, neocortical-control and sham operated rats received shock on alternate trials during a 10-day classical conditioning period. Heart rate during prestimulus, stimulus and post-shock periods was evaluated. Hippocampal rats did not show prestimulus heart rate patterning resulting from the shock-no shock sequence of trials as did the other two groups. The tachycardic response to the stimulus, however, was the same in all groups. During 5 days of extinction, all groups showed a reduced response to the stimulus and the prestimulus rates for the 3 groups were equivalent. Since these findings were not accompanied by differences in heart rate response to the shock or in activity, it may be concluded that the effect of hippocampal lesions was to reduce the animal's sensitivity to the reinforcement schedule while not affecting heart rate response attenuation during extinction.