Journal of neurophysiology
-
1. In early local feedback models for controlling horizontal saccade amplitude, a feedback signal of instantaneous eye position is continuously subtracted from a reference signal of desired eye position at a comparator. The output of the comparator is dynamic motor error, the remaining distance the eyes must rotate to reach the saccadic goal. ⋯ Moreover, the peak velocity-amplitude relationships, the instantaneous velocity profiles, and the ratio of horizontal and vertical velocities and durations were very similar to those of visually guided saccades. 7. Independent comparator models can readily account for the ability to manipulate the amplitude of one component of oblique saccades without affecting the other. However, two-dimensional local feedback models that cannot exert independent control over the horizontal and vertical amplitudes of oblique saccades should be carefully reevaluated.
-
Comparative Study
Presynaptic A1 inhibitory/A2A facilitatory adenosine receptor activation balance depends on motor nerve stimulation paradigm at the rat hemidiaphragm.
1. Adenosine modulates acetylcholine (ACh) release from the rat motor nerve terminals. Tonic activation of presynaptic A1 inhibitory and/or A2A facilitatory adenosine receptors is regulated by the concentration of the nucleoside at the synapse. ⋯ In contrast, the inhibitory effect of the A1 receptor agonist R-N6-phenylisopropyladenosine was significantly attenuated in both stimulation conditions. 6. In conclusion, the results suggest that high-intensity, high-frequency motor nerve stimulation critically influences endogenous adenosine formation and the A1/A2A receptor activation balance, i.e., it potentiates the tonic adenosine A2A-receptor-mediated facilitation of ACh release, whereas activation of the inhibitory A1 receptors becomes less effective. A model is proposed that attempts to further elucidate adenosine's involvement in synaptic transmission adaptation.
-
1. The introduction of a period of darkness between the disappearance of an initial fixation target and the appearance of a peripheral saccade target produces a general reduction in saccadic reaction time (SRT)-known as the gap effect- and often very short latency express saccades. To account for these phenomena, premotor processes may be facilitated by release of visual fixation and advanced preparation of saccadic programs. ⋯ These findings indicate that training-dependent express saccades are restricted to a specific spatial location dictated by the training target, and their incidence is facilitated by high predictability of target presentation, long-duration foreperiod, absence of visual fixation, eccentric initial eye position opposite to the saccade direction, and express saccade occurrence in the previous trial. The release of fixation afforded by the gap accounts for the general gap effect, but has only a modulatory influence on express saccade generation. We conclude that advanced motor preparation of saccadic programs generally reduces SRT and is primarily responsible for the occurrence of express saccades, which therefore may be caused mainly by neuronal changes restricted to a specific locus-coding for the trained movemen
-
Comparative Study Clinical Trial
Response compatibility and the relationship between event-related potentials and the timing of a motor response.
1. Earlier studies have shown that changes in the difficulty of sensory discrimination in a choice reaction time task result in a prolongation of the peak latency for several components of the long-latency event-related potential (ERP). With the use of the technique of response-locked averaging, we have previously shown that manipulation of the difficulty of sensory discrimination also affects response execution as assessed by the interval between the ERP and onset of the response. ⋯ However, despite the similarly tight coupling of the response to the ERP in both the compatible and noncompatible conditions, the response occurred later relative to the ERPs in the noncompatible condition. This suggests that different components of the ERP are responsible for triggering the response in different circumstances. Our observations on the error trials suggests that the decision to respond (on these trials) is based on the occurrence of cerebral events that are evoked by either rare or frequent stimuli, whereas this decision (on correct response trials) is based on cerebral events elicited only by the rare stimuli.
-
1. The role of descending brain stem modulatory systems in the development of persistent behavioral hyperalgesia and dorsal horn hyperexcitability was studied in rats with unilateral hindpaw inflammation. Inflammation was induced by intraplantar injection of complete Freund's adjuvant (CFA, 0.05 ml of an 1:1 oil/saline emulsion, 25 micrograms Mycobacterium), or lambda carrageenan (1 mg/ 0.1 ml saline). ⋯ Thoracic saline did not produce a significant change in the receptive field size (105 +/- 9%, n = 4). The increases in responses to noxious thermal and mechanical stimuli after thoracic lidocaine block were also significantly greater in inflamed than in noninflamed rats (P < 0.01). There was no significant difference in the increase in responses to electrical stimulation of the sciatic nerve after lidocaine between inflamed and noninflamed rats.(ASTRACT TRUNCATED)