Saccadic eye movements

Behavioral Function in Adults. Neurobehavioral testing has revealed effects in adults at PbB levels (i.e., 40-80 pg/dL) below those causing encephalopathy (>400 pg/dL). Evaluations of occupationally exposed adults include several affected parameters at PbB levels between 40 and 80 pg/dL. Disturbances in oculomotor function (saccadic eye movements) in lead workers with mean PbB levels of 57-61 pg/dL were reported in a study by Baloh et al. (1979) with follow-up by Spivey et al. (1980) and in a study by Glickman et al. (1984). Deficits in hand-eye coordination and reaction time were reported in 190 lead-exposed workers (mean PbB level, 60.5 pg/dL) (NIOSH 1974). Most of the workers had been exposed for between 5 and 20 years. A similar study, however, reported no differences... 

Glickman L, Valciukas JA, Lilis R, et al. 1984. Occupational lead exposure Effects on saccadic eye movements, lnt Arch Occup Environ Health 54 115-125. 

Oliva GA, Bucci MP, Fioravanti R. (1993). Impairment of saccadic eye movements by scopolamine treatment. Percept Motor Skills 159-67. 

Amongst other subcortical structures, neurons of the superior colliculus are involved in saccadic eye movements and attentional processes (Wurtz et al., 1982). Local deactivation of the superior colliculus decreases attentional task performance only in the presence of distractors. Again there appears to be a critical interaction between attention and arousal, with a specific attentional role for this particular locus remaining unclear. 

Saccadic eye movements Fast conjugate eye movements, e.g. when reading or following moving objects A few minutes... 

Blom, M.W. et al., Tire effects of alprazolam, quazepam and diazepam on saccadic eye movements, parameters of psychomotor function and the EEG, Fund. Clin. Pharmacol., 4, 653, 1990. 

The basal ganglia are part of what is referred to as the brain s extrapyra-midal system of motor control, so called to distinguish it from the pyramidal nerve tracts that control voluntary movement. The extrapyra-midal system is most directly associated with involuntary aspects of movement such as muscle tone and posture. However it has extensive connections with other parts of the brain, especially the frontal cortex, the seat of personality and rationality. This functional network... mediates volitional motor activity, saccadic eye movements, emotion, motivation, cognition and social behaviour (Wonodi, Hong, Thaker 2005, p. 340). Thus conditions that effect neurotransmission in the basal ganglia can be expected to have far-reaching functional consequences. 

Shimo Y, Hikosaka O (2001) Role of tonically active neurons in primate caudate in reward-oriented saccadic eye movement. J Neurosci 27 7804-7814. 

Additional doses of benzodiazepines in long-term users are commonly needed, but it is unknown whether these additional doses have any effect. The effects of an additional 20 mg dose of oxazepam has been assessed in a double-bhnd, balanced-order, crossover, randomized study in 16 long-term users of oxazepam and 18 benzodiazepine-naive controls (5). The effects of oxazepam 10 and 30 mg were assessed on (a) saccadic eye movements as a proxy for the sedative effect (b) the acoustic startle response as a proxy for the anxiolytic effects (c) memory (d) reaction time tasks (e) subjective measurements. There were dose-related effects on the peak velocity of saccadic eye movement and response probability and on the peak amplitude of the acoustic startle response. Comparison with the controls suggested that the sedative effects might be confounded with the suppression of sedative withdrawal symptoms, whereas the patients were as sensitive as the controls to the effects of an additional dose of oxazepam on the acoustic startle response. 

The quinidine derivative hydroquinidine had some beneficial effects in 10 patients with myotonic dystrophy with slow saccadic eye movements, apathy, and hjrper-somnia (42,43). However, two patients had nausea and epigastric pain and withdrew while taking the active treatment. Although there were no cases of cardiac abnormalities, the authors raised the concern that in patients with myotonic dystrophy, who have a high frequency of cardiac disturbances, the risk of cardiac... 

Di Costanzo A, Mottola A, Toriello A, Di lorio G, Tedeschi G, Bonavita V. Does abnormal neuronal excitability exist in myotonic dystrophy I. Effects of the antiarrhythmic drug hydroquinidine on slow saccadic eye movements. Neurol Sci 2000 21(2) 73-80. 

In a double-blind, placebo-controlled, crossover study, 10 patients with probable progressive supranuclear palsy took single oral doses of zolpidem (5 and 10 mg), co-careldopa (levodopa 250 mg plus carbidopa 25 mg), or placebo in four separate trials in random order (10). Zolpidem, unlike levodopa or placebo, reduced voluntary saccadic eye movements, and the 5 mg dose produced a statistically significant improvement in motor function. The adverse effects of zolpidem included drowsiness and... 

Studies have shown a reduced density of lymphocyte BZ receptor sites (119) and platelet BZ sites in GAD patients, which was increased following diazepam treatment (120). These peripheral receptors are pharmacologically distinct tfom the central GABA receptors, so the relevance of these studies to anxiety is unclear. More relevant may be the study cf central BZR activity in anxiety patients. Reduced BZR sensitivity has been shown in GAD patients by measuring saccadic eye movements (121,122). This effect was even more pronounced in patients with panic disorder G23), but was absent in OCD (124). These studies suggest that there may be a reduced BZ receptor function in some anxiety disorders. 

Search is an active process in any inspection context. The item or process inspected must be searched in stages. At times these stages ctm involve moving an area of limited extent across the item, as in using a flashlight to inspect the inside of an aircraft fuel tank or a microscope s limited field of view to cover the whole area of a microchip. Within a field of view, a target is visible to the inspector only within a limited area, called the visual lobe. This visual lobe must be actively moved in successive fixations across the field of view with saccadic eye movements. Within a single visual lobe, information can only be extracted at a limited rate (Eriksen 1990), so that an attention area can be said to move successively within the visual lobe. 

FIGURE 16.1 Main sequence diagrams, (a) peak velocity-saccade magnitude, (b) saccade duration-saccade magnitude, and (c) latent period-saccade magnitude for 54 saccadic eye movement by a single subject. (From Enderle, J.D. 1988. Aviation, Space, Environ. Med. 59 309-313. With permission.)... 

The first quantitative saccadic eye movement model, iUustrated in Figure 16.2, was pubHshed by Westheimer [1954]. Based on visual inspection of a recorded 20° saccade, and the assumption of a step controller, Westheimer proposed the following second order model ... 

FIGURE 16.5 Saccadic eye movement in response to a 15° target movement. Solidline is the prediction of the saccadic eye movement model with the final parameter estimates computed using the system identification techniques. Dots are the data. (From Enderle, J.D. and Wolfe, J.W. 1987. IEEE Trans. Biomed. Eng. 34 43-55. With permission.)... 

Another Linear Homeomorphic Saccadic Eye Movement Model... 

The previous linear model of the oculomotor plant is derived from a nonlinear oculomotor plant model by Hsu et al. [1976], and based on a linearization of the force-velocity curve [Bahill et al., 1980). Muscle viscosity traditionally has been modeled with a hyperbolic force-velocity relationship. Using the linear model of muscle reported by Enderle and coworkers [1991], it is possible to avoid the linearization, and derive an updated linear homeomorphic saccadic eye movement model. 

Saccadic eye movements simulated with this model have characteristics which are in good agreement with the data, including position, velocity and acceleration, and the main sequence diagrams. 

Subsequently, a number of other investigators have modified the local feedback mechanism proposed by Robinson [1975] to better describe the neural connections and firing patterns of brainstem neurons in the control of horizontal saccadic eye. In addition to the Robinson model, two other models describe a saccade generator [Scudder, 1988 Scudder et al., 2002 Enderle, 1994, 2002], AH of the models involve three types of premotor neurons burst, tonic, and pause cells, as previously described, and involve a pulse-step change in firing rate at the motoneuron during a saccadic eye movement. 

FIGURE 16.13 Simulated eye position in solid line shown in top graph, generated with EBN saccadedata (shown in lower graph) and the oculomotor plant in Figure 16.8. Actual eye movement data recorded with the EBN dataduringa saccadic eye movement. (Data provided by Dr. David Sparks from his laboratory while at the University of Alabama.)... 

Enderle, J.D. 1994. A physiological neural network for saccadic eye movement control Armstrong Laboratory/AO-TR-1994-0023. Air Force Material Command, Brooks Air Force Base, Texas. 

Enderle, J.D. and Wolfe, J.W. 1988. Frequency response analysis of human saccadic eye movements. Comput. Biol. Med. 18 195-219. 

Enderle, J.D. 1988. Observations on pilot neurosensory control performance during saccadic eye movements. Aviation, Space Environ. Med. 59 309-313. 

Westheimer, G. 1954. Mechanism of saccadic eye movements. AMA Archiv. Ophthalmol. 52 710-724. Wilkie, D.R. 1968. Muscle Studies in Biology, Vol. 11. Edward Arnold Ltd., London, United Kingdom. 

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