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The effect of a unilateral ablation of the occipital lobe on pattern discrimination in the rabbit
Behavioural Brain Research, 3 (1981) 401M04 © Elsevier/North-Holland Biomedical Press
401
The effect of a unilateral ablation of the occipital lobe on pattern discrimination in the rabbit
M.W. VAN HOF and P.M. S T U U R M A N
Dept. of Physiology 1, Erasmus Universi O, Rotterdam, P.O. Box 1738, 3000 DR Rotterdam ( The Netherlands) (Received February 12th, 1981) (Revised version received March 5th, 1981) (Accepted March 5th, 1981)
Key words. pattern discrimination - occipital lobe lesion - rabbit
Binocular brightness and striated pattern discrimination were studied in Dutch-belted rabbits. A comparison was made between normal animals and animals in which a unilateral lesion of the occipital lobe had been made three months after birth. No difference between the two groups was found in brightness discrimination learning. However, normal animals were found to do better both in acquisition and accuracy of striated pattern discrimination.
Following a unilateral ablation of the occipital cortex, pattern discrimination with the eye contralateral to the lesion has been found to be severely impaired [6]. In the present experiments we studied what effect such a lesion has on binocular pattern discrimination. Forty Dutch-belted rabbits, bred in the laboratory, were used. In 20 animals a unilateral lesion of the occipital lobe was made when they were 3 months old [3]. The remainder served as unoperated control animals. For all animals pattern discrimination experiments were started when they were 5 months old. The pattern discrimination apparatus and the shaping procedure have been described elsewhere [4, 5, 7]. Throughout training 100 trials were given per day and the food-rewarded pattern was placed randomly either left or right. At first the animals were trained on a brightness discrimination. The white target was rewarded. After the 900/o correct criterion was reached on two consecutive days, the animals were trained to discriminate vertical vs horizontal striations. The vertical striations were rewarded. After that, the minimal angular difference which could be detected by the animals was determined. A total of 2500 trials of vertical vs oblique striations was given. The angular differences used were 45 °, 25 °, 15°, 10 ° and 5 °. Each angular difference was given for 5 daily sessions
402
150-
÷
111
z 0 100
i
ILl 1--
0 ~-
50
gO
0
n~ n~ uJ
0
O
N=20
O
O
N=20
Fig. 1. Average number of errors to criterion and standard errors for brightness discrimination in normal and operated animals.
of 100 trials. The vertical striations were always rewarded. In random sequence the oblique striations were rotated either clockwise or counter-clock~se. In Fig. 1 the result of the brightness discrimination are shown. The average number of errors made before criterion was reached was not significantly different between groups. However, with vertical vs horizontal discrimination the ablated animals made significantly more errors (Fig. 2). In Fig. 3 the results obtained with angular differences of 45 ° and less are shown. For each animal the average score for the last two days of each angular difference was obtained and combined to provide an average value for the group. In agreement with previous experiments [8], normal animals reached high scores with angular differences down to 10°. However, it was found that operated animals reached significantly lower scores at angular differences of 25 °, 15 ° and 10° (Student's t-test P = 0.01). For each animal the 7 5 ~ correct value was determined by means of a linear interpolation method [8]: The average 75~o correct value was smaller in normal animals than in operated ones (9.55°+ 0.95 ° (S:E.) and 14.99°+ 1.43 (S.E.)). With the Student's t-test this was a significant difference at the P = 0.01 level. In other words, although both groups did equally well on a brightness discrimination task, they differed in acquisition and performance accuracy of striated pattern discriminations.
403
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100
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0
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Fig. 2. Average number of errors to criterion and standard errors for vertical vs horizontal striation discrimination in normal and operated animals.
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Z
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0 o
~
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Fig. 3. The percentage of correct choices at various angular differences in normal and operated animals.
It has been shown [1, 2] that in the rabbit bilateral removal of the visual cortex leads to severe impairment of pattern discrimination, but does not affect brightness discrimination. This means that in the rabbit, after a unilateral lesion of the occipital lobe, the overall visual field for brightness discrimination is fully intact. On the other hand, the animals will be hemianopic for pattern discrimination. A likely explanation for the defects of pattern discrimination
404 after unilateral ablation of the occipital lobe seems to be that in this situation the animal must make use of a demanding motor strategy in order !~ compare the patterns. 1 De Vos-Korthals, W.H. and Van Hof, M.W., Pattern discrimination after unilateral and bilateral ablation of the occipital lobe in the rabbit, Behav. Brain Res., 2 (1981) 219 222. 2 Murphy, E.H. and Chow, K.L. Effects of striate and occipital cortical lesic~ns on visual discrimination in the rabbit, Exp. Neurol., 42 (1974) 78 -88. 3 Stuurman, P.M. and Van Hof, M.W., Pattern discrimination in rabbits kept in environments of different complexities after unilateral removal of the occipital cortex, Behaw Brain Res., 1 (1980) 211.-226. 4 Van der Mark, F. and Meyer, J.H.C., Automatic control of installations for- experiments relating to physiological research of the visual system, Comput. Prog. Biol. Med., 4 (1974) 3541. 5 Van Hof, M.W., Discrimination between striated patterns of different orientation in the rabbit, Vision Res., 6 (1966) 89-94. 6 Van Hof, M.W. and Lagers-Van Haselen, G.C., Monocular pattern discrimination in rabbits after unilateral ablation of the visual cortex, Exp. Neurol., 46 (1975) 257-259. 7 Van Hof, M.W. and Russell, I.S., Binocular vision in the rabbit, Physiol. Betu~v., 19 (1977) 121 128. 8 Van Hof, M.W. and Wiersma, C.A.G., The angular threshold of discrimination for striated patterns of different orientation in the rabbit, Vision Res., 7 (1967) 265-270.
401
The effect of a unilateral ablation of the occipital lobe on pattern discrimination in the rabbit
M.W. VAN HOF and P.M. S T U U R M A N
Dept. of Physiology 1, Erasmus Universi O, Rotterdam, P.O. Box 1738, 3000 DR Rotterdam ( The Netherlands) (Received February 12th, 1981) (Revised version received March 5th, 1981) (Accepted March 5th, 1981)
Key words. pattern discrimination - occipital lobe lesion - rabbit
Binocular brightness and striated pattern discrimination were studied in Dutch-belted rabbits. A comparison was made between normal animals and animals in which a unilateral lesion of the occipital lobe had been made three months after birth. No difference between the two groups was found in brightness discrimination learning. However, normal animals were found to do better both in acquisition and accuracy of striated pattern discrimination.
Following a unilateral ablation of the occipital cortex, pattern discrimination with the eye contralateral to the lesion has been found to be severely impaired [6]. In the present experiments we studied what effect such a lesion has on binocular pattern discrimination. Forty Dutch-belted rabbits, bred in the laboratory, were used. In 20 animals a unilateral lesion of the occipital lobe was made when they were 3 months old [3]. The remainder served as unoperated control animals. For all animals pattern discrimination experiments were started when they were 5 months old. The pattern discrimination apparatus and the shaping procedure have been described elsewhere [4, 5, 7]. Throughout training 100 trials were given per day and the food-rewarded pattern was placed randomly either left or right. At first the animals were trained on a brightness discrimination. The white target was rewarded. After the 900/o correct criterion was reached on two consecutive days, the animals were trained to discriminate vertical vs horizontal striations. The vertical striations were rewarded. After that, the minimal angular difference which could be detected by the animals was determined. A total of 2500 trials of vertical vs oblique striations was given. The angular differences used were 45 °, 25 °, 15°, 10 ° and 5 °. Each angular difference was given for 5 daily sessions
402
150-
÷
111
z 0 100
i
ILl 1--
0 ~-
50
gO
0
n~ n~ uJ
0
O
N=20
O
O
N=20
Fig. 1. Average number of errors to criterion and standard errors for brightness discrimination in normal and operated animals.
of 100 trials. The vertical striations were always rewarded. In random sequence the oblique striations were rotated either clockwise or counter-clock~se. In Fig. 1 the result of the brightness discrimination are shown. The average number of errors made before criterion was reached was not significantly different between groups. However, with vertical vs horizontal discrimination the ablated animals made significantly more errors (Fig. 2). In Fig. 3 the results obtained with angular differences of 45 ° and less are shown. For each animal the average score for the last two days of each angular difference was obtained and combined to provide an average value for the group. In agreement with previous experiments [8], normal animals reached high scores with angular differences down to 10°. However, it was found that operated animals reached significantly lower scores at angular differences of 25 °, 15 ° and 10° (Student's t-test P = 0.01). For each animal the 7 5 ~ correct value was determined by means of a linear interpolation method [8]: The average 75~o correct value was smaller in normal animals than in operated ones (9.55°+ 0.95 ° (S:E.) and 14.99°+ 1.43 (S.E.)). With the Student's t-test this was a significant difference at the P = 0.01 level. In other words, although both groups did equally well on a brightness discrimination task, they differed in acquisition and performance accuracy of striated pattern discriminations.
403
IllU--
150-
-I-
z O
f
100
uJ I--
0 0 ~(D
50
n.,
0
n,." n."
u.I
{}b ii{
0
0
N=20
0
0
N=20
Fig. 2. Average number of errors to criterion and standard errors for vertical vs horizontal striation discrimination in normal and operated animals.
O3
1°°1 ~
Z
80-
0 o
~
7060-
Z uJ
(.9 n~
50I
450
250
1150 1'00 5 o
Fig. 3. The percentage of correct choices at various angular differences in normal and operated animals.
It has been shown [1, 2] that in the rabbit bilateral removal of the visual cortex leads to severe impairment of pattern discrimination, but does not affect brightness discrimination. This means that in the rabbit, after a unilateral lesion of the occipital lobe, the overall visual field for brightness discrimination is fully intact. On the other hand, the animals will be hemianopic for pattern discrimination. A likely explanation for the defects of pattern discrimination
404 after unilateral ablation of the occipital lobe seems to be that in this situation the animal must make use of a demanding motor strategy in order !~ compare the patterns. 1 De Vos-Korthals, W.H. and Van Hof, M.W., Pattern discrimination after unilateral and bilateral ablation of the occipital lobe in the rabbit, Behav. Brain Res., 2 (1981) 219 222. 2 Murphy, E.H. and Chow, K.L. Effects of striate and occipital cortical lesic~ns on visual discrimination in the rabbit, Exp. Neurol., 42 (1974) 78 -88. 3 Stuurman, P.M. and Van Hof, M.W., Pattern discrimination in rabbits kept in environments of different complexities after unilateral removal of the occipital cortex, Behaw Brain Res., 1 (1980) 211.-226. 4 Van der Mark, F. and Meyer, J.H.C., Automatic control of installations for- experiments relating to physiological research of the visual system, Comput. Prog. Biol. Med., 4 (1974) 3541. 5 Van Hof, M.W., Discrimination between striated patterns of different orientation in the rabbit, Vision Res., 6 (1966) 89-94. 6 Van Hof, M.W. and Lagers-Van Haselen, G.C., Monocular pattern discrimination in rabbits after unilateral ablation of the visual cortex, Exp. Neurol., 46 (1975) 257-259. 7 Van Hof, M.W. and Russell, I.S., Binocular vision in the rabbit, Physiol. Betu~v., 19 (1977) 121 128. 8 Van Hof, M.W. and Wiersma, C.A.G., The angular threshold of discrimination for striated patterns of different orientation in the rabbit, Vision Res., 7 (1967) 265-270.