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The field potential profile during activation of the avian optic tectum
Author(s) -
Holden A. L.
Publication year - 1968
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1968.sp008395
Subject(s) - optic tectum , neuroscience , field (mathematics) , biology , medicine , retina , mathematics , pure mathematics
1. The field potential profile resulting from electrical stimulation of the optic nerve‐head was recorded with micro‐electrodes inserted radially into the pigeon optic tectum. 2. The first response, in the superficial tectum, was a graded negative wave, the N‐wave. Its latency was 2·3 msec, S.D. 0·22 msec. The wave form underwent an abrupt polarity reversal in the R‐zone, to yield a graded positive wave, the P‐wave, in deeper laminae. The P‐wave had a latency of 2·0 msec, S.D. 0·16 msec. 3. Both N‐wave and P‐wave showed a graded increase in amplitude as stimulating current was increased. On any given track this increase occurred over a similar range of stimulating current. 4. In many tracks the rise‐time and duration of the N‐wave were independent of amplitude. 5. The rise‐time of the P‐wave was longer, and its duration was shorter, than the rise‐time and duration of the N‐wave. This effect was shown to be due to two successive sinks occurring superficially to the P‐zone. 6. Depth profiles also showed these two sinks, separately located in the N‐zone and R‐zone. 7. To paired stimuli the N‐wave showed refractoriness at intervals of 2‐4·5 msec, facilitation at intervals up to 25 msec, and subsequent depression. It showed low‐frequency depression at 10 and 20/sec. 8. The R‐zone was localized by a lesion technique to sub‐layers d to g of the stratum griseum et fibrosum superficiale. Thus the tissue negativity was closely co‐extensive with the anatomical distribution of optic nerve terminals. 9. It is suggested that the N‐wave is the sink of excitatory synaptic potentials produced in the superficial tectum, and predictions relating unitary firing to the field potential profile are made.