Sinusoidal Target Motion Research Articles

Properties of pursuit movements.

This chapter describes dynamic properties of smooth pursuit, visual and non-visual stimuli for pursuit, smooth eye-head tracking movements, and plastic-adaptive properties of pursuit. Step-ramp visual stimulus motion has revealed important properties of pursuit, including the latency to onset, initial acceleration, accuracy, and transient oscillations-all features that have been used to develop models of the pursuit system, discussed in the chapter "Models of pursuit" by Robinson. The role of predictive neural mechanisms in generating pursuit movements that anticipate target motion, and that enable near-perfect tracking of sinusoidal target motion, are examined. Smooth pursuit can be generated in response to targets that do not move, such as stroboscopic lights and images stabilized in the periphery of vision. The view that, during combined eye-head pursuit, the pursuit signal is used to cancel the vestibulo-ocular reflex is an incomplete hypothesis, contradicted by behavioral and electrophysiological findings. Smooth pursuit shows adaptive capabilities, evident in individuals who develop extraocular muscle palsies.

Information fusion control with time delay for smooth pursuit eye movement

Smooth pursuit eye movement depends on prediction and learning, and is subject to time delays in the visual pathways. In this paper, an information fusion control method with time delay is presented, implementing smooth pursuit eye movement with prediction and learning as well as solving the problem of time delays in the visual pathways. By fusing the soft constraint information of the target trajectory of eyes and the ideal control strategy, and the hard constraint information of the eye system state equation and the output equation, optimal estimations of the co‐state sequence and the control variable are obtained. The proposed control method can track not only constant velocity, sinusoidal target motion, but also arbitrary moving targets. Moreover, the absolute value of the retinal slip reaches steady state after 0.1 sec. Information fusion control method elegantly describes in a function manner how the brain may deal with arbitrary target velocities, how it implements the smooth pursuit eye movement with prediction, learning, and time delays. These two principles allowed us to accurately describe visually guided, predictive and learning smooth pursuit dynamics observed in a wide variety of tasks within a single theoretical framework. The tracking control performance of the proposed information fusion control with time delays is verified by numerical simulation results.

Optimizing geometric accuracy of four-dimensional CT scans acquired using the wall- and couch-mounted Varian® Real-time Position Management™ camera systems.

The aim of this study was to identify sources of anatomical misrepresentation owing to the location of camera mounting, tumour motion velocity and image processing artefacts in order to optimize the four-dimensional CT (4DCT) scan protocol and improve geometrical-temporal accuracy. A phantom with an imaging insert was driven with a sinusoidal superior-inferior motion of varying amplitude and period for 4DCT scanning. The length of a high-density cube within the insert was measured using treatment planning software to determine the accuracy of its spatial representation. Scan parameters were varied, including the tube rotation period and the cine time between reconstructed images. A CT image quality phantom was used to measure various image quality signatures under the scan parameters tested. No significant difference in spatial accuracy was found for 4DCT scans carried out using the wall- or couch-mounted camera for sinusoidal target motion. Greater spatial accuracy was found for 4DCT scans carried out using a tube rotation speed of 0.5 s rather than 1.0 s. The reduction in image quality when using a faster rotation speed was not enough to require an increase in patient dose. The 4DCT accuracy may be increased by optimizing scan parameters, including choosing faster tube rotation speeds. Peak misidentification in the recorded breathing trace may lead to spatial artefacts, and this risk can be reduced by using a couch-mounted infrared camera. This study explicitly shows that 4DCT scan accuracy is improved by scanning with a faster CT tube rotation speed.

Ultrasound tracking for intra-fractional motion compensation in radiation therapy

Modern techniques as ion beam therapy or 4D imaging require precise target position information. However, target motion particularly in the abdomen due to respiration or patient movement is still a challenge and demands methods that detect and compensate this motion. Ultrasound represents a non-invasive, dose-free and model-independent alternative to fluoroscopy, respiration belt or optical tracking of the patient surface. Thus, ultrasound based motion tracking was integrated into irradiation with actively scanned heavy ions. In a first in vitro experiment, the ultrasound tracking system was used to compensate diverse sinusoidal target motions in two dimensions. A time delay of ∼200 ms between target motion and reported position data was compensated by a prediction algorithm (artificial neural network). The irradiated films proved feasibility of the proposed method. Furthermore, a practicable and reliable calibration workflow was developed to enable the transformation of ultrasound tracking data to the coordinates of the treatment delivery or imaging system – even if the ultrasound probe moves due to respiration. A first proof of principle experiment was performed during time-resolved positron emission tomography (4DPET) to test the calibration workflow and to show the accuracy of an ultrasound based motion tracking in vitro. The results showed that optical ultrasound tracking can reach acceptable accuracies and encourage further research.

Rapid learning of pursuit target motion trajectories revealed by responses to randomized transient sinusoids

When humans pursue sinusoidal target motion they rapidly learn to track with minimal phase error despite inherent visuo-motor processing delays; prior evidence suggests that prediction might even occur within the first cycle. Here, this has been examined by evoking reactive responses to single cycle stimuli having randomised periodicity and peak velocity. Periodicity was varied within three specific ranges with differing average periodicity. Initial responses in the first half-cycle were remarkably similar within periodicity ranges, irrespective of target velocity or frequency, but differed between ranges. In contrast, in the second half-cycle eye velocity closely matched the target in velocity and timing, irrespective of differences in eye velocity in the first half. Abrupt transitions occurred between first and second half-cycles, consistent with the hypothesis that target motion information is sampled and stored within the first half-cycle, irrespective of actual eye velocity evoked, and then released as a predictive estimate in the second half.

TU‐G‐BRC‐09: A Comparison of Step‐And‐Shoot and DMLC IMRT‐Delivery for Real‐Time Tumor Tracking

Purpose: The dose distributions of static and dynamically delivered IMRT fields for real‐time target tracking were evaluated to determine which methods work best for the compensation of breathing‐induced organ motion.Methods: A single IMRT beam of a clinical plan was applied with the step‐and‐shoot delivery technique and the sliding‐window technique with the research Siemens 160MLC in order to account for a two‐dimensional, sinusoidal target motion and for a real patient breathing‐curve. For the sliding‐window dose delivery, two different maximum leaf speeds, as well as synchronized and non‐synchronized leaf trajectories were employed. All fields were delivered without and with tracking of the target using three electromagnetic transponders of the Calypso‐System. The dose distributions were measured with radio‐chromic films in a water equivalent phantom in 5cm depth and were compared to the step‐and‐shoot delivery for a non‐moving phantom. For the dose comparison a gamma criterion of 2%/2mm was utilized.Results: For both motions tracking improved the gamma‐index by 13%–32%. For the dynamic delivery no significant advantage was observed between unsynchronized and synchronized leaf trajectories. Moreover no remarkable differences were found by comparing results obtained with different maximum leaf speeds. For both target motions the step‐and‐shoot delivery shows a better dose distribution using the tracking approach: For the 2D‐motion a gamma‐passing rate of 86.3% can be achieved using step‐and‐shoot compared to 78.2% on average for the dynamic dose delivery. For the patient breathing‐motion 83.3% compared to an average of 77.1% were obtained. When comparing the results of both motion patterns, slightly higher passing rates were found with the periodic 2D‐sinusoidal motion. Conclusions: Only small differences were observed for different IMRT dose delivery modes with organ motion tracking, except for the tracked step‐and‐shoot delivery. However, more experiments have to be performed to investigate other IMRT plans and explicit dependencies on the field modulation.Supported by Siemens Healthcare/CR

Feasibility study of multi-pass respiratory-gated helical tomotherapy of a moving target via binary MLC closure

Gated radiotherapy of lung lesions is particularly complex for helical tomotherapy, due to the simultaneous motions of its three subsystems (gantry, couch and collimator). We propose a new way to implement gating for helical tomotherapy, namely multi-pass respiratory gating. In this method, gating is achieved by delivering only the beam projections that occur within a respiratory gating window, while blocking the rest of the beam projections by fully closing all collimator leaves. Due to the continuous couch motion, the planned beam projections must be delivered over multiple passes of radiation deliveries. After each pass, the patient couch is reset to its starting position, and the treatment recommences at a different phase of tumour motion to ‘fill in’ the previously blocked beam projections. The gating process may be repeated until the plan dose is delivered (full gating), or halted after a certain number of passes, with the entire remaining dose delivered in a final pass without gating (partial gating). The feasibility of the full gating approach was first tested for sinusoidal target motion, through experimental measurements with film and computer simulation. The optimal gating parameters for full and partial gating methods were then determined for various fractionation schemes through computer simulation, using a patient respiratory waveform. For sinusoidal motion, the PTV dose deviations of −29 to 5% observed without gating were reduced to range from −1 to 3% for a single fraction, with a 4 pass full gating. For a patient waveform, partial gating required fewer passes than full gating for all fractionation schemes. For a single fraction, the maximum allowed residual motion was only 4 mm, requiring large numbers of passes for both full (12) and partial (7 + 1) gating methods. The number of required passes decreased significantly for 3 and 30 fractions, allowing residual motion up to 7 mm. Overall, the multi-pass gating technique was shown to be a promising way to reduce the impact of lung tumour motion during helical tomotherapy.

Incorporating Prediction in Models for Two-Dimensional Smooth Pursuit

A predictive component can contribute to the command signal for smooth pursuit. This is readily demonstrated by the fact that low frequency sinusoidal target motion can be tracked with zero time delay or even with a small lead. The objective of this study was to characterize the predictive contributions to pursuit tracking more precisely by developing analytical models for predictive smooth pursuit. Subjects tracked a small target moving in two dimensions. In the simplest case, the periodic target motion was composed of the sums of two sinusoidal motions (SS), along both the horizontal and the vertical axes. Motions following the same or similar paths, but having a richer spectral composition, were produced by having the target follow the same path but at a constant speed (CS), and by combining the horizontal SS velocity with the vertical CS velocity and vice versa. Several different quantitative models were evaluated. The predictive contribution to the eye tracking command signal could be modeled as a low-pass filtered target acceleration signal with a time delay. This predictive signal, when combined with retinal image velocity at the same time delay, as in classical models for the initiation of pursuit, gave a good fit to the data. The weighting of the predictive acceleration component was different in different experimental conditions, being largest when target motion was simplest, following the SS velocity profiles.

MO‐D‐M100J‐06: Reducing Intra‐Fraction Organ Motion Effects Using Segment Size Constraint in Direct Aperture Optimization

Purpose: In IMRT delivery, an important issue is intra‐fraction organ motion, which causes significant degradation of the delivered dose. Some simulation researches have showed that organ motion effects could be significantly reduced by increasing the segment size. In this study, a direct aperture optimization based commercial inverse planning system was modified to assess the clinical impact of creating optimized plans with segment size constraints (SSC). Our study seeks to answer what price in static plan quality one has to pay to avoid dose degradation in moving targets? Method and Materials: IMRT plans with and without SSC were optimized for two abdominal cases using static CT images. The MLC travel direction is aligned with the projected motion direction and SSC penalizes all MLC leaf openings smaller than twice the projected motion amplitude. Static plans were recalculated with a sinusoidal target motion with 1cm amplitude and 4second period. Results: In both cases with and without SSC, PTV volume covered by 95% of the prescribed dose (V95) was less than 1%, indicating that SSC had little effect on static plan quality. After incorporating target motion, V95 was improved by applying SSC, with the degree of improvement depending on the particular case. For case 1, V95 improved from 84.5% to 93.3% by adding SSC. Further study shows that dose coverage of peripheral PTV regions improved more significantly with SSC than central regions. In all plans, differences of the doses to the critical structures were within a few percent. By adding SSC, the treatment plan was more tolerant to target motion. Conclusions: Our study showed that when segmental IMRT plans were delivered to a moving target, SSC improves delivered dose conformity (V95) as much as 9% without significantly sacrificing static plan quality. Peripheral PTV shows more improvement in dose coverage with SSC than central regions.

SU‐FF‐J‐100: Normal Tissue Dose in Abdomen Under Dynamic Beam Tracking

Purpose: Dynamic beam tracking has been proposed for moving targets. Since planning systems consider all structures stationary, the tracking delivery is purposely different from the plan. This study evaluated the dosimetric differences in normal tissue between the stationary beam plan and the dynamic beam delivery. Method and Materials: IMRT plans for abdominal cancers were generated without considering organ motion. A margin of 1 cm, rather than the conventional 1.5 to 2cm, was used. The resulting MLC sequences were converted to dynamic sequences to track a hypothetical sinusoidal target motion of ±2cm in superior/inferior direction and ±1.5 cm in anterior/posterior direction. A 4‐second respiration cycle and 400 MU/minute dose rate were also assumed. To assess the worst‐case scenario of normal tissue dose difference, all normal structures including liver, kidneys, small bowel and spinal cord were assumed stationary. Doses recalculated using the dynamic sequences were compared with that of the original IMRT plan. Results: As expected, dynamic beam tracking maintained target dose coverage while substantially reduced doses to surrounding normal structures. The differences in normal tissue dose between the stationary beam plan and the moving beam plan were small. The low‐dose volume was increased while the high‐dose volume was decreased slightly in normal tissue with dynamic beam tracking. No degradation of normal structure sparing was observed although the structures were not moving with the target. Conclusion: Contrary to our intuitions, dynamic beam tracking does not significantly alter the normal tissue dose in the abdomen as compared with optimized plans using stationary beams. Unsynchronized motion between the target and normal structures did not cause higher doses to the normal structures when tracking is focused on the target. MLC sequences of the optimized stationary plans can be used for dynamic beam tracking using a simple conversion into dynamic sequences that follows tumor motion.

Human Hand Moves Proactively to the External Stimulus: An Evolutional Strategy for Minimizing Transient Error

We investigated particularly the proactive nature of the visual-motor system by steady and transient experiments of a hand-tracking task, and confirmed that the hand motion precedes on the average the target motion in steady runs within a finite frequency range of the sinusoidal target motion. The question why and how much the hand motion should precede was answered by frequency-jump experiments. The results implied that the positive phase shift of the hand motion represents the proactive nature of the visual-motor control system which is adaptationally developed for each person to minimize the transient error of the hand motion when the target motion changes unexpectedly.

Predictive responses of periarcuate pursuit neurons to visual target motion.

The smooth pursuit eye movement system uses retinal information about the image-slip-velocity of the target in order to match the eye-velocity-in-space (i.e., gaze-velocity) to the actual target velocity. To maintain the target image on the fovea during smooth gaze tracking, and to compensate for the long delays involved in processing visual motion information and/or eye velocity commands, the pursuit system must use prediction. We have shown recently that both retinal image-slip-velocity and gaze-velocity signals are coded in the discharge of single pursuit-related neurons in the simian periarcuate cortex. To understand how periarcuate pursuit neurons are involved in predictive smooth pursuit, we examined the discharge characteristics of these neurons in trained Japanese macaques. When a stationary target abruptly moved sinusoidally along the preferred direction at 0.5 Hz, the response delays of pursuit cells seen at the onset of target motion were compensated in succeeding cycles. The monkeys were also required to continue smooth pursuit of a sinusoidally moving target while it was blanked for about half of a cycle at 0.5 Hz. This blanking was applied before cell activity normally increased and before the target changed direction. Normalized mean gain of the cells' responses (re control value without blanking) decreased to 0.81(+/-0.67 SD), whereas normalized mean gain of the eye movement (eye gain) decreased to 0.65 (+/-0.16 SD). A majority (75%) of pursuit neurons discharged appropriately up to 500 ms after target blanking even though eye velocity decreased sharply, suggesting a dissociation of the activity of those pursuit neurons and eye velocity. To examine whether pursuit cell responses contain a predictive component that anticipates visual input, the monkeys were required to fixate a stationary target while a second test laser spot was moved sinusoidally. A majority (68%) of pursuit cells tested responded to the second target motion. When the second spot moved abruptly along the preferred direction, the response delays clearly seen at the onset of sinusoidal target motion were compensated in succeeding cycles. Blanking (400-600 ms) was also applied during sinusoidal motion at 1 Hz before the test spot changed its direction and before pursuit neurons normally increased their activity. Preferred directions were similar to those calculated for target motion (normalized mean gain=0.72). Similar responses were also evoked even if the second spot was flashed as it moved. Since the monkeys fixated the stationary spot well, such flashed stimuli should not induce significant retinal slip. These results taken together suggest that the prediction-related activity of periarcuate pursuit neurons contains extracted visual components that reflect direction and speed of the reconstructed target image, signals sufficient for estimating target motion. We suggest that many periarcuate pursuit neurons convey this information to generate appropriate smooth pursuit eye movements.

Ocular Pursuit Responses to Repeated, Single-Cycle Sinusoids Reveal Behavior Compatible With Predictive Pursuit

The link between anticipatory smooth eye movements and prediction in sinusoidal pursuit was investigated by presentation of series of identical, single-cycle, sinusoidal target motion stimuli. Stimuli occurred at randomized intervals (1.2-2.8 s) but were preceded by an audio warning cue 480 ms before each presentation. Cycle period (T) varied from 0.64 to 2.56 s and target displacement from 4 to 20 degrees in separate series. For T </= 1.28 s, responses to the first stimulus of each series exhibited a time delay across the whole cycle (mean = 121 ms for T = 0.8 s). But, in the second and subsequent (steady-state) presentations, anticipatory movements, proportional to target velocity, were made and time delay was significantly reduced (mean = 43 ms for T = 0.8 s). Steady-state time delays were comparable to those evoked during continuous sinusoidal pursuit and less than pursuit reaction time. Even when subjects did not follow the target in the first presentation, they responded to the second presentation with reduced time delay. Throughout the experiments, three types of catch trial (A-C) were introduced. In A, the target failed to appear as expected after the warning cue. Anticipatory smooth movements were initiated, reaching a peak velocity proportional to prior target velocity around 200 ms after expected target onset. In B, the target stopped midway through the cycle. Even if the target remained on and was stationary, the eye movement continued to be driven away from the stationary target with a velocity similar to that of prior responses, reaching a peak velocity that was again proportional to expected target velocity after >/=205 ms. In C, the amplitude of the single sinusoid was unexpectedly increased or decreased. When it decreased, eye velocity throughout the first half-cycle of the response was close to that executed in response to prior stimuli of higher velocity and did not return to an appropriate level for 382-549 ms. Conversely, when amplitude increased, eye velocity remained inappropriately low for the first half-cycle. Results of A and C indicate that subjects are able to use velocity information stored from prior presentations to initiate an oculomotor drive that predominates over visual feedback for the first half-cycle. Results of B indicate that the second part of the cycle is also preprogrammed because it continued despite efforts to suppress it by fixation. The results suggest that initial retinal velocity error information can be sampled, stored, and subsequently replayed as a bi-directional anticipatory pattern of movement that reduces temporal delay and could account for predictive control during sinusoidal pursuit.

Directional organization of eye movement and visual signals in the floccular lobe of the monkey cerebellum.

The floccular lobe of the monkey is critical for the generation of visually-guided smooth eye movements. The present experiments reveal physiological correlates of the directional organization in the primate floccular lobe by examining the selectivity for direction of eye motion and visual stimulation in the firing of individual Purkinje cells (PCs) and mossy fibers. During tracking of sinusoidal target motion along different axes in the frontoparallel plane, PCs fell into two classes based on the axis that caused the largest modulation of simple-spike firing rate. For "horizontal" PCs, the response was maximal during horizontal eye movements, with increases in firing rate during pursuit toward the side of recording (ipsiversive). For "vertical" PCs, the response was maximal during eye movement along an axis just off pure vertical, with increases in firing rate during pursuit directed downward and slightly contraversive. During pursuit of target motion at constant velocity, PCs again fell into horizontal and vertical classes that matched the results from sinusoidal tracking. In addition, the directional tuning of the sustained "eye velocity" and transient "visual" components of the neural responses obtained during constant velocity tracking were very similar. PCs displayed very broad tuning approximating a cosine tuning curve; the mean half-maximum bandwidth of their tuning curves was 170-180 degrees. Other cerebellar elements, related purely to eye movement and presumed to be mossy fibers, exhibited tuning approximately 40 degrees narrower than PCs and had best directions that clustered around the four cardinal directions. Our data indicate that the motion signals encoded by PCs in the monkey floccular lobe are segregated into channels that are consistent with a coordinate system defined by the vestibular apparatus and eye muscles. The differences between the tuning properties exhibited by PCs compared with mossy fibers indicate that a spatial transformation occurs within the floccular lobe.

Quantitative analysis of smooth pursuit eye movement

Abnormalities of smooth pursuit eye movement (SPEM) have been estimated, mainly using the wave form on an electro-oculogram, in a qualitative way. Many methods for quantitative analysis of SPEM have been designed, though most are still uncommon in present clinical use. Using a personal computer, we developed a method of automatic quantitative analysis of ocular tracking eye movement recorded by electro-oculography (EOG). The design concept of this method is based on the observation that eye movement during ocular tracking consists of two different kinds of eye movements, one is SPEM and the other is saccade. The combination of SPEM and saccade (composite eye movement: CEM) commonly appears during ocular tracking. These two kinds of eye movement are essentially different not only in behavior but also about involved neural pathway in the central nervous system. From this point of view, we believe that the two kinds of eye movements involved in ocular tracking should be evaluated separately. The analysis method is outlined as follows. A horizontal sinusoidally moving visual target was employed to elicit ocular tracking eye movements. The test frequencies were set at 0.1, 0.2, 0.4 and 0.8Hz, and the amplitude of target motion was 15 deg at each frequency. The 20 seconds of eye movement data measured by EOG were fed into the computer through a digital-analog converter for further analysis. Using our original saccade detection algorithm, based on the physiological behavior of saccades, the saccadic components were detected and removed from the eye movement wave. The remaining parts, fragments of SPEM, were connected by means of interpolating defective parts. The reconstructed wave was a slow cumulative eye position curve (SCEP). Sinusoidal target motion, CEM and SCEP were processed by the FFT (Fast Fourier Transformation) method. Bode plots were applied to summarize the gain and phase of responses to SCEP and the target motion wave. These processes enable us to estimate abnormalities of SPEM such as low gain, abnormal phase shift and large trends in tested duration. We conclude that the method described here is useful for quantitative estimation of SPEM in clinical neuro-otological examinations.

Participation of the caudal fastigial nucleus in smooth-pursuit eye movements. I. Neuronal activity.

1. We recorded single-unit activity from neurons of an output of the cerebellum, the fastigial nucleus, in two rhesus macaques while the monkeys tracked small moving targets with their eyes. Many neurons in the caudal part of the fastigial nucleus exhibited a modulation in their discharge rates when smooth-pursuit eye movements were elicited by either sinusoidal or step-ramp motions of a small target. 2. The pursuit direction that elicited the most vigorous modulation in unit firing to sinusoidal target motion could be horizontal, vertical, or oblique. Most often, the preferred direction was in the contralateral and/or downward direction (50 of 69 neurons) or in the ipsilateral and/or upward direction (13 of 69). 3. For units whose preferred smooth-pursuit directions were either contralateral/downward or ipsilateral/upward during sinusoidal pursuit, peak firing as measured by the phase shift of periodic modulation at 0.5-0.8 Hz occurred near the time of peak velocity. The discharge of 80% of the neurons with contralateral/downward preferred directions preceded eye velocity by an average of -27 degrees; thus these neurons discharged maximally during eye acceleration. In contrast, neurons with ipsilateral/upward preferred directions lagged peak velocity by an average of +10.5 degrees and therefore discharged during eye deceleration. 4. The average eye velocity sensitivity for sinusoidal pursuit between 0.5 and 0.8 Hz was 0.83 +/- 0.57 (SD) spikes/s per degrees/s. We also tested 36 units during pursuit at a variety of frequencies in their preferred directions and found that firing rates increased monotonically with peak eye velocity. However, the firing rate saturated at velocities ranging from 20 to 60 degrees/s for different units. 5. When a monkey tracked a step-ramp target motion, three discharge patterns emerged in the 27 units tested. Just over half of the units discharged a burst of spikes that preceded (average lead of 27.4 +/- 17 ms) and lasted throughout the initial third of the eye acceleration; the burst was followed by a subsequent steady firing that continued after the eye had accelerated to its steady velocity. Fewer neurons discharged a burst that began late in the acceleration and was followed by steady firing. Occasional neurons showed only a gradual increase in firing rate during acceleration followed by a steady discharge. 6. Thirty of the 31 fastigial smooth-pursuit units tested also were modulated during sinusoidal yaw and/or pitch oscillations while the animals fixated a spot that rotated with them.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses during eye movements of brain stem neurons that receive monosynaptic inhibition from the flocculus and ventral paraflocculus in monkeys.

1. We have identified a group of brain stem cells called "flocculus target neurons" (or FTNs) because they are inhibited at monosynaptic latencies by stimulation of the flocculus and the ventral paraflocculus with single electrical pulses. We report the responses of FTNs, as well as those of other brain stem cells, during horizontal eye movements with the head stationary and during natural vestibular stimulation in monkeys. 2. FTNs discharged primarily in relation to eye movements. The majority (71%) showed increased firing for eye movement away from the side of the recording ("contraversive"), which is consistent with their inhibition by Purkinje cells that show increased firing for eye movement toward the side of recording. However, a significant and surprisingly large percentage (29%) of FTNs showed increased firing for eye movement toward the side of recording ("ipsiversive"). 3. The firing rate of FTNs showed strong modulation during pursuit of sinusoidal target motion with the head stationary and during the compensatory eye movements evoked by fixation of an earth-stationary target with sinusoidal head rotation. In addition, firing rate was related to eye position during steady fixation at different positions. Of the FTNs that showed increased firing for contraversive eye motion during pursuit with the head stationary, most had an infection in the relationship between firing rate and eye position so that the sensitivity to eye position was low for eye positions ipsilateral to straight-ahead gaze and high for eye positions contralateral to straight-ahead gaze. 4. When the monkey canceled the vestibuloocular reflex (VOR) by tracking a target that moved exactly with him during sinusoidal head rotation, the firing rate of FTNs was modulated much less strongly than during pursuit with the head stationary. In the FTNs that showed increased firing for contraversive eye motion during pursuit, firing rate during cancellation of the VOR increased for contraversive head motion during sinusoidal vestibular rotation at 0.4 Hz but was only weakly modulated during rotation at 0.2 Hz. 5. The position-vestibular-pause cells (PVP-cells), previously identified as interneurons in the disynaptic VOR pathways, were not inhibited by stimulation of the flocculus and ventral paraflocculus and had response properties that were different from FTNs. The majority (69%) showed increased firing for contraversive eye motion during pursuit and for ipsiversive head motion during cancellation of the VOR, whereas some (31%) showed the opposite direction preferences under both conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Normalization of deficient P50 auditory sensory gating in schizophrenic patients and their first degree relatives by nicotine

Smooth pursuit eye movements (SPEM) were assessed in 30 schizophrenic patients, 12 lithium-free manic patients, and 20 normal controls. Compared to schizophrenic patients, manic patients evidenced less SPEM impairment in an attention enhancing, sinusoidal target motion condition and had superior performance during a visual fixation condition. SPEM and visual fixation dysfunctions may be more common in schizophrenic than in acutely manic patients, even when the latter are characterized by marked attentional dysfunction, poor interepisode psychosocial functioning, and psychosis.

Initiation of sinusoidal tracking eye movements in man.

Smooth pursuit eye movement was recorded with a DC amplifier during horizontal sinusoidal target motion at 0.3, 0.6, 0.8, 1.0 and 1.2 Hz and a peak-to-peak amplitude of 20 degrees. Eye movement was digitalized at 100 Hz and 12 bits. From the digitalized eye movements, the maximum position error, the correlation coefficient and regression coefficients between stimulus and eye position were calculated in each half cycle. The A/D conversion and calculation were performed using a 16 bit microcomputer (NEC PC 98). Thirteen healthy volunteers with normal smooth pursuit patterns were examined. The correlation coefficient increased, but the maximum position error and the two regression coefficients decreased as the target moved. However, all four stabilized from about the 3rd half cycle regardless of the target frequency. These findings indicate that the smooth pursuit of a sinusoidally moving target reaches the maintenance at about the 3rd half cycle after initiation of two half cycles from the beginning of the target motion. This might be due to a prediction (or learning) of periodicity.

Specificity of smooth pursuit eye movement and visual fixation abnormalities in schizophrenia: Comparison to mania and normal controls

Smooth pursuit eye movements (SPEM) were assessed in 30 schizophrenic patients, 12 lithium-free manic patients, and 20 normal controls. Compared to schizophrenic patients, manic patients evidenced less SPEM impairment in an attention enhancing, sinusoidal target motion condition and had superior performance during a visual fixation condition. SPEM and visual fixation dysfunctions may be more common in schizophrenic than in acutely manic patients, even when the latter are characterized by marked attentional dysfunction, poor interepisode psychosocial functioning, and psychosis.