160
Horst Bleckrnann et al.
cms- 1 ) two types of units immediately became apparent. Depending on flow
direction (anterior-to-posterior vs. posterior-to-anterior), type I units responded to
water flow with an increase or decrease of ongoing activity. If the direction of flow
was such that ongoing activity was increased, the responses to a vibrating sphere
were masked (Fig. 5). The ongoing activity of type II units barely changed in
response to water flow. Consequently responses of type II units to a vibrating
sphere stimulus were not masked (Fig. 5). There are many indications that type I
units innervate superficial and type II units canal neuromasts.
A
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~Fig. 5 A, B. Responses of goldfish PLLN fibers to ten repetitions of a 50 Hz constantamplitude sine wave stimulus (I 00 ~m p-p displacement amplitude) generated by a
vibrating sphere of 8 mm diameter without background water flow (left) and in the
presence of a 10 cms- 1 DC background flow (right) . Flow direction was from anterior to
posterior. Raster diagrams and the corresponding PST histograms (binwidth 5 ms) are
shown. A Responses of a type I unit. B Responses of a type II unit. Note that the
background flow masks the responses of type I units but not those of type II units. (Data
kindly provided by J. Engelmann)