Behavioral estimates of absolute threshold in rat

AbstractDark-adapted thresholds of albino and pigmented rats were estimated using behavioral methods. Albino and pigmented rats who had been water deprived learned to bar press for water reinforcement when a light stimulus was presented. Absolute threshold was defined to be the light intensity at which bar pressing behavior was significantly modified by the presence of the light stimulus. Albino rats had an average threshold of −5.23 log cd/m2 and the pigmented rats had a threshold of −5.0 log cd/m2. These values are close to −5.3 log cd/m2, the psychophysical threshold of human observers in the same apparatus. Consistent with our earlier electrophysiology, these behavioral experiments provide no evidence for an albino/pigmented sensitivity difference. Comparisons are made between behavioral and electrophysiological determinations of absolute threshold in albino and pigmented rats. Thresholds determined behaviorally agree remarkably well with those derived from visual evoked potentials.

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Visual thresholds in albino and pigmented rats

Visual Neuroscience ◽

10.1017/s0952523800010816 ◽

1992 ◽

Vol 9 (3-4) ◽

pp. 409-414 ◽

Cited By ~ 23

Author(s):

Pilar Herreros De Tejada ◽

Daniel G. Green ◽

Carmen Muñoz Tedó

Keyword(s):

Evoked Potentials ◽

Superior Colliculus ◽

Absolute Threshold ◽

Albino Rats ◽

Response Curves ◽

Albino Rat ◽

A Value ◽

Visual Evoked Cortical Potential ◽

Single Unit Recordings ◽

Visual Evoked

AbstractAlbino rats have recently been reported to have increment thresholds against dim backgrounds that are two log units higher than those of pigmented rats. We, on the other hand, have failed to confirm these differences using electroretinogram b waves and pupillary light reflexes. This paper reports on experiments using evoked potentials from cortex and colliculus and single-unit recordings from colliculus.We recorded visual-evoked potentials from cortex and superior colliculus in the strains of albino (CD) and pigmented (Long-Evans) rats used in the earlier studies. Thresholds were determined on eight fully dark-adapted animals by extrapolating intensity-response curves to the point at which there was zero evoked potential. The average dark-adapted threshold for the visual-evoked cortical potential was —5.26 log cd/m2in pigmented and —5.80 log cd/m2 in albino animals. The average dark-adapted threshold for the superior colliculus evoked response was —5.54 log cd/m2 in pigmented and —5.84 log cd/m2 in albinos. The differences were not statistically significant. On the same apparatus, the average absolute threshold for three human observers was —5.3 log cd/m2, a value close to the rat dark-adapted thresholds. Thus, visual-evoked cortical potentials and superior collicular evoked potentials failed to confirm the report of higher dark-adapted thresholds for albinos. In addition, we find that single units in superior colliculus in the albino rat respond to very dim flashes.

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