Third-order auditory neurons in the avian nucleus laminaris (NL) are the first to receive binaural input. In the chick, NL consists of a monolayer of neurons with polarized dendritic arbors oriented dorsally and ventrally. Afferents from second-order neurons in the ipsilateral nucleus magnocellularis (NM) innervate the dorsal dendrites of NL neurons, distributing processes of approximately equal length to NL neurons along an isofrequency band (roughly caudomedial to rostrolateral). Afferents from the contralateral NM innervate the ventral dendrites of NL neurons, distributing collateral branches sequentially as they proceed from caudomedial to rostrolateral along the isofrequency band of neurons. This innervation pattern could be the basis of a “delay line” circuit, as postulated in models of neural networks mediating sound localization. We examined this circuit by analyzing evoked field potentials using a brain slice preparation containing both NL and NM. The results were consistent with the previous anatomical findings. When the ipsilateral auditory nerve or ipsilateral NM was stimulated, there was no consistent variation in the latency of postsynaptic field potentials across the medial-to-lateral extent of NL. In contrast, when the contralateral NM or NM axons in the crossed dorsal cochlear tract were stimulated, a linear increase in the latency of postsynaptic potentials was observed from medial to lateral positions in NL. When stimulation amplitudes for both the ipsilateral and contralateral inputs were adjusted so as to produce little or no postsynaptic field potential, simultaneous bilateral stimulation evoked a pronounced response. Thus, NL neurons can act as “coincidence detectors.” The amplitude of the postsynaptic response was dependent on the relative timing of stimulation of the two inputs. The optimal time difference changed systematically across the medial-to-lateral extent of NL. This system of delay lines and coincidence detectors could provide a mechanism for converting interaural time differences into a “place map” within NL.

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Necrotizing fasciitis is a destructive soft tissue infection that rarely involves the eyelids. Three cases of necrotizing fasciitis of the eyelids are described. Necrotizing fasciitis was preceded by minor forehead soft tissue trauma in two cases and occurred spontaneously in one. In two patients necrotizing fasciitis was bilateral and involved both the upper and lower eyelids. Review of these cases, in addition to 18 cases previously reported in the English literature, reveals a predominance in females, preceding minor local soft tissue trauma, frequent bilateral involvement, and an association with alcohol abuse and diabetes. In all of the patients, group A beta-hemolytic streptococci were cultured from the wound. Early recognition of the disease process, prompt surgical debridement of the necrotic tissue, aggressive antimicrobial therapy, and delayed skin grafting combine to minimize morbidity.

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