j *@ - Sociedade Brasileira de Psicologia

FACILITATION IN INSECT PHOTOREUEPTORS
DORA FlX VENTURA
Universidade de Sâo Paulo
INTRODUW ION
In 1954 a surprising phenomenon was reported by Ruck and Jphn on an
hwertebrate preparation:if a strong flashwas presented to the eye the eledroretinogrnm
(ERG) response to a succeeding equaly strong flash was increased, not decreased, as
' would be expected. In the human visual system, our subjective experience when
presented witl the light of a briglt flash is of a trnnqient blindness, which im plies the
satmation of the neural network from the retina to the central nervous system . Not
only at saturation levels, but also below, light adaptation has been shown to reduce
sensitivity in m zmerous psychophysical ahd electrophysiological experiments. As a
result, the theories about the functioning of the receptor meghanism have been always
based on the reduction of sensitivity, due to light adaptation. It Fas therefore a
startling surprise that an eye could $ve a peater response after a supposedly blinding
light. 'l'he effect was called facilitation by the authors.
The study of this effect was not, however, pmsued any ftlrther at that time,
and this report by Ruck and Jnhn (1954) did not receive much atention in the '
literature.
Fae tation in the ERG of xveral sN des
It was only in the late sixties and early seventies that the subjed was studied
again. Several authors reported facilitation in other invertebratrs besides the small
crmtacean Lygia ocddentalîs used by Ruck and Jnhn (1954). lt was found in the ERG
of several species (locmt: Giulio ald Lucaroni, 1967 ; fly and beetle: Dudek and
Koopowitz, 1972, Dudek, 1975 ; ants: Ventura et al., 1976, Ventura and Puglia, 1977,
Ventura, 1983; spider: Ynmashita and Tateda, 1976 and a crustacean, Strétten and
Ogden, 1971).
0. own work in ants 1ed to the conclusion that, at least in the species Atta
sexdens, facilitation is just as important as adaptation since it covers a sensitivitf range
tlut is about eqlml to that covered by adaptation. 'lhis is to say that sensitivity in the
ant ERG can be menipulated by experimental stimulation propammes to either
increase (fadlitation) or decrease (adaptation) by the same extent. Facilitation,
however, is not jlzst the reverse of adaptation. It has different properties with resped
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