Saccades

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... 

Rothenberg SJ Charles R. Drew University of Medicine Science, Los Angeles, CA The role of prepregnancy maternal bone lead and prenatal maternal blood lead upon alterations in infant saccadic and smooth pursuit eye movements National Institute of General Medical Sciences... 

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. 

Ocular Effects. Vision was blurred in 15 of the 23 workers examined as a result of intermediate-or chronic-duration inhalation exposures to high blood concentrations (in excess of 2 pg/L) of chlordecone during its production. The effects on vision were characterized by a disruption of ocular motility following a horizontal saccade by rapid random multidirectional eye movements. Visual acuity and smooth eye movements were unaffected (Taylor 1982, 1985). The rapid eye movements were probably due to disturbance of the brain stem. 

Saccades are also affected by anticholinergic hallucinogens in humans (Oliva et al. 1993). Increases in saccade duration and latency occur along with decreases in velocity. Postsaccadic fixation is impaired as well, where the eye drifts after reaching the target. 

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. 

Funahashi, S., Chafee, M.V., and Goldman-Rakic, P.S. (1993) Prefrontal neuronal activity in rhesus monkeys performing a delayed anti-saccade task. Nature 365 753-756. 

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

Motor, executive functions Slower saccades. Some impairment, especially in complex tasks No effect... 

But that s not all. There s the REM enhancement effect, too. Serotonin plays an active role in the regulation of the brain stem saccade generator. This is the automatic brain stem system by which we make the continuous involuntary eye movements necessary to waking vision. This saccade... 

Now Schenck, Mahowald, and others tell us that not only does SSRI treatment potentiate eye movements in NREM sleep, but that it may also potentiate dream enactment in REM sleep. In other words, SSRIs may induce the REM sleep behavior disorder How does this work In addition to releasing the saccade generator from inhibition, the drug appears to interfere with the spinal cord inhibitory mechanism that normally blocks the central motor commands that so convincingly animate our dreams but do not result in real behavior. 

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. 

Reverse transcriptase Saccade Enzyme that forms complementary DNA (cDNA). Abrupt, high velocity eye movement produced by a precisely timed pattern of activity in the motor neurons innervating the extraocular muscles. 

Opsoclonus is a disorder of eye movement characterized by multidirectional saccades. Opsoclonus is usually associated with myoclonus, constituting OM, and there are often coexisting signs of cerebellar dysfunction and encephalopathy. The causation of OM is complex, including viral, metabolic, toxic, and structural disorders. Paraneoplastic OM was first described in children. Neuroblastoma is found in 50% of the pediatric OM cases, but on the whole, only 2-3% of all children with neuroblastic tumors have paraneoplastic OM [74, 75]. 

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. 

Head-twitches Presence Rapid saccadic side-to-side axial movements of the head... 

Smooth-pursuit eye movement task IV 0.1 mg/kg 12 J, leading saccades 4 ratio for slowly moving targets Avila et al. (2002)... 

Effects of ketamine on leading saccades during smooth-pursuit eye movements may implicate cerebellar dysfunction in schizophrenia. Am J Psychiatry 159 1490-1496. 

Breitmeyer B, Ganz L. 1976. Implications of sustained and transient channels for theories of visual pattern masking, saccadic suppression and information processing. Psychol Rev 83 1-36. 

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

Hikosaka O, Wurtz RH (1983) Visual and oculomotor functions of monkey substantia nigra pars reticulata. I. Relation of visual and auditory responses to saccades. J Neurophysiol 49 1230-1253. 

Similar results have been forthcoming from primate studies. Thus, D1 receptor antagonists administered iontophoretically to the PFC enhance, rather than impair, stimulus processing by single units in delayed saccade paradigms (Williams and Goldman-Rakic,... 

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