The effect of retinal illumination and retinal blockade on synaptic transmission in the lateral geniculate nucleus of the cat

A review of special education law

Children with disabilities require special education and related services that are as diverse as the individual children themselves. Special education is not necessarily a special classroom but a well thought-out program of collaborative interventions leading to educational goals set forth by a multidisciplinary team. Effective special education is guided by both state and federal laws that protect the rights of the child and encourage certain universal core principles. Special-needs children are entitled to a free and appropriate education with related services in the least restrictive environment. Pediatricians and pediatric subspecialists are in a unique position to develop a medical home for the disabled child, and in doing so must be well-versed in both case law and federal legislation as it applies to special education, in an effort to be a child's best advocate. A chronological review of case law and federal legislation, including the Individuals with Disabilities Education Act, No Child Left Behind Act, and recent amendments, are discussed, and their relevance to physician practice is detailed.

Circadian rhythms in synaptic excitability of the dorsal lateral geniculate nucleus in the rat

Excitability changes of the dorsal lateral geniculate nucleus were recorded in male albino rats (Wistar strain) with chronically implanted electrodes. Both averaged postsynaptic and presynaptic evoked responses showed clear circadian rhythms under a constant dark condition. The circadian rhythmicity of the evoked responses was not as a result of motor activity or due to the sleep-wakefulness changes which might show circadian rhythms independently. Circadian rhythms of antidromic and orthodromic evoked responses were abolished after bilateral suprachiasmatic nucleus lesions. These results suggest that the circadian rhythm generated in the suprachiasmatic nucleus significantly affects visual information transmission in the lateral geniculate nucleus.

Tonic retinal influences in primates

A type of unit discharge, termed "luxotonic," has been found in the striate cortex of unanesthetized squirrel monkeys and macaques.6, 21 The firing frequency of these units shows relatively little adaptation, continues indefinitely (hours), and reflects the level of diffuse illumination of the eye. The more numerous "photergic" units discharge more rapidly in the light, whereas "scotergic" units fire fastest in the dark (or at luminance levels below threshold for cones). Luxotonic activity is abolished by anesthesia and has not been described for striate cortex of other species. Primates also display a profound alteration in the EEG of striate cortex following elimination of all retinal input.32 Since this change is far more drastic than that produced by blindness in other species, it is natural to inquire whether it is related to the loss of the normally prominent luxotonic activity. When the blind monkey sleeps, the bizarre EEG is replaced by patterns wholly normal in appearance,32 indicating that some nonvisual system has extensive access to striate cortex in this state.

Influence of eye movements on geniculo-striate excitability in the cat

1. The excitability of the geniculo-striate pathway during a saccadic eye movement was studied in alert cats with chronically implanted electrodes. Excitability was assessed by the amplitude of post-synaptic components of field responses in both lateral geniculate nucleus and visual cortex to electrical stimulation of the optic chiasm. Modifications in amplitude were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in the electrooculograms and altering delays in the stimulus pulse.2. The post-synaptic component of the geniculate response was markedly depressed for about 150 msec, reaching a trough at approximately 100 msec after the initiation of an eye movement. This effect was dependent on the visual environment and was not observed in complete darkness. A similar depression occurred when the visual field was abruptly moved by retinal impulses generated by a quick displacement of the image of the visual world associated with an eye movement. The depression reflected a reduction of cellular discharge to the orthodromic volley and hence a suppression of the transmission of visual information through the lateral geniculate nucleus. This may be a mechanism for saccadic suppression.3. The post-synaptic components of the cortical response were enhanced for about 200 msec, reaching a peak at approximately 150 msec after the initiation of an eye movement. Although this facilitation occurred also in complete darkness, it did not occur when the visual field was abruptly shifted while the eyes were stationary. The fact that it occurred with eye movements and exclusively in the post-synaptic components suggests that it was caused by signals from a system closely related to eye movements. This may be a manifestation of the corollary mechanism.