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ABSTRACT: The smooth pursuit system interacts with the vestibular system to maintain the accuracy of eye movements in space. To understand neural mechanisms of short-term modifications of the vestibulo-ocular reflex (VOR) induced by pursuit-vestibular interactions, we used a cross-axis procedure in trained monkeys. We showed earlier that pursuit training in the plane orthogonal to the rotation plane induces adaptive cross-axis VOR in complete darkness. To further study the properties of adaptive responses, we examined here the initial eye movements during tracking of a target while being rotated with a trapezoidal waveform (peak velocity 30 or 40 degrees/s). Subjects were head-stabilized Japanese monkeys that were rewarded for accurate pursuit. Whole body rotation was applied either in the yaw or pitch plane while presenting a target moving in-phase with the chair with the same trajectory but in the orthogonal plane. Eye movements induced by equivalent chair rotation with or without the target were examined before and after training. Before training, chair rotation alone resulted only in the collinear VOR, and smooth eye movement-tracking of orthogonal target motion during rotation had a normal smooth pursuit latency (ca 100 ms). With training, the latency of orthogonal smooth tracking eye movements shortened, and the mean latency after 1 h of training was 42 ms with a mean gain, at 100 ms after stimulus onset, of 0.4. The cross-axis VOR induced by chair rotation in complete darkness had identical latencies with the orthogonal smooth tracking eye movements, but its gains were <0.2. After cross-axis pursuit training, target movement alone without chair rotation induced smooth pursuit eye movements with latencies ca 100 ms. Pursuit training alone for 1 h using the same trajectory but without chair rotation did not result in any clear change in pursuit latency (ca 100 ms) or initial eye velocity. When a new target velocity was presented during identical chair rotation after training, eye velocity was correspondingly modulated by just 80 ms after rotation onset, which was shorter than the expected latency of pursuit (ca 100 ms). These results indicate that adaptive changes were induced in the smooth pursuit system by pursuit-vestibular interaction training. We suggest that this training facilitates the response of pursuit-related neurons in the cortical smooth pursuit pathways to vestibular inputs in the orthogonal plane, thus enabling smooth eye movements to be executed with shorter latencies and larger eye velocities than in normal smooth pursuit driven only by visual feedback.
Experimental Brain Research 08/2001; 139(4):473-81. · 2.39 Impact Factor
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ABSTRACT: Repetitive, brief target ramp movements every few seconds lead to anticipatory acceleration before each ramp onset and anticipatory deceleration before ramp offset. We assessed whether identifying novel changes in the pursuit target would alter this pattern of anticipatory pursuit. Without target identification (TI), anticipatory acceleration increased when intervals between ramps were regular, rather than random. It increased further when, between ramps, the target was invisible rather than stationary and visible. Anticipatory deceleration increased when the target was expected to stop rather than disappear at ramp offset. For TI trials, the pursuit target changed briefly into a Landolt C acuity target that had to be identified. Compared to no TI, anticipatory acceleration decreased when a stationary C always appeared just before ramp onset. It increased when a moving C appeared just after ramp onset, but only when the target was invisible between ramps. Anticipatory deceleration was reduced when a moving C appeared just before ramp offset, but did not increase when a stationary C appeared just after ramp offset. The changes were significant, but of small magnitude, suggesting that predictive pursuit, especially with a visible target between ramps, cannot be greatly influenced by attempts to selectively improve acuity at a particular phase of the stimulus.
Vision Research 09/1999; 39(16):2767-75. · 2.41 Impact Factor
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ABSTRACT: Anticipatory smooth pursuit before the expected appearance of a moving target can reduce the initial retinal blur caused by the 100-ms delay of visual feedback. Humans, though, can only voluntarily generate smooth velocities up to about 5 degrees/s without a moving target. However, previous experiments have shown that repetitive brief presentations of a moving target every few seconds appear to charge an internal store, the contents of which can later be released to generate higher velocity anticipatory movements. This store's longevity was assessed here by repetitively presenting a moving target for 500 ms at different known intervals up to 7.2 s. Target motion at 25 degrees/s or 50 degrees/s was tested, with presentations in alternate directions or the same direction. Anticipatory velocity, measured 100 ms after target onset, decreased with increasing interval for all target motion conditions. A decrease was still seen when accurate timing cues were given before each presentation, suggesting that the drive for anticipatory pursuit is held in a short-term store lasting a few seconds which can enhance the low velocities produced by volition alone. The results also demonstrate that high-velocity anticipatory pursuit helps to overcome the temporal delays in the system and allows target velocity to be matched at an earlier time.
Experimental Brain Research 06/1998; 120(1):129-33. · 2.39 Impact Factor
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ABSTRACT: Retrotransposition has been well documented as a significant source of mutagenesis in diverse eukaryotic organisms, including humans. Insertions of retrotransposons within or in close proximity to transcription units cause many spontaneous mutations, and have been implicated as a source of heritable genetic defects and as a cause of carcinogenesis. The mechanisms by which retrotransposon insertions produce mutant phenotypes are diverse and, in many cases, not fully understood. A model transcriptional system was utilized to test the effects of copia retrotransposon-derived sequence insertions upon gene expression in different cellular environments. The results of these experiments indicate that retrotransposon insertions within nontranslated regions of a transcription unit inhibit gene expression by at least two concurrently acting mechanisms: 1) transcriptional interference due to an active internal promoter and, 2) trans RNA hybridization interactions between transcripts containing complementary retrotransposon sequences.
Cellular and molecular biology 05/1992; 38(2):159-69. · 0.98 Impact Factor
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BioTechniques 05/1990; 8(4):390-1. · 2.67 Impact Factor
