Indian Institute of Technology, Kharagpur,
1 Rajghat Education Centre, Varanasi and
2 M. G. Kashi Vidyapeeth, Varanasi, India
Received 5 January 2000; in revised form 13 March 2000; accepted 27 March 2000
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ABSTRACT |
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INTRODUCTION |
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The present study made an attempt to examine the different forms of side-bias in addition to handedness in drug addicts of certain kinds, with a specific aim to assess their pattern of functional lateralization. Side-bias is considered to be an indicator of functional cerebral lateralization. Although investigators make a distinction between limb (hand, foot) and sense organ (eye, ear) lateralizations, these indices (especially handedness) in essence are taken up as the relatively stable indicators of behavioural asymmetry akin to cerebral lateralization. It was postulated in the present study that drug addicts would exhibit atypical (anomalous) side-bias in comparison to normal controls. The confirmation of the hypothesis would allow us to investigate the possible association between side-bias and drug addiction. Geschwind and Galaburda (1985) envisaged the association between non-right handedness and addiction proneness behaviour as a function of maturational defect at the pre-natal level of the individual.
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SUBJECTS AND METHODS |
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Addicts receiving out-patient hospital treatment during the ages 1545 years were invited to participate in the study. Patients with hand tremor or with known organic pathology were excluded. Addicts older than 45 years were excluded, to avoid any confounding effect of age on the pattern of handedness. It has been observed that the incidence of left handedness decreases with the increase in age, in particular at an upper level (Coren and Halpern, 1991).
Procedure
Side-bias questionnaires (Mandal et al., 1992a,b
) were used to assess the degree of preference for all four measures: hand (22 items: writing, eating, throwing a ball, lifting a bucketful of water, using a spoon to stir, keying a lock, using scissors, painting, threading a needle, combing, brooming, winding a clock, screwing a nut, hammering a nail, opening a tap, switching the light, lighting a matchstick, toothbrushing, sorting cards, using a knife, using a racket for games, unscrewing a jar), foot (five items: kicking a ball, foot extended to get into a bus, foot on which body weight rested in standing posture, stepping over an obstacle, foot extended in long jump), eye (five items: looking through a telescope, snapping a photograph, gunshooting, looking through a keyhole, preferred eye to wink), ear (five items: listening on the telephone when both hands are free, hearing a pocket radio, matching musical tone, sensing tick movement in wrist watch, listening to a low voice). Subjects were asked to indicate their preference for an activity in the questionnaire on a 5-point rating scale (1 = never, 2 = rarely, 3 = occasionally, 4 = frequently, 5 = always) for both sides, left and right, separately and independently in each instance.
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RESULTS |
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Footedness
Identical analysis with foot preference as the dependent measure yielded a non-significant main effect of Group, but a significant effect of Side. Foot bias was significantly more for the right (mean 4.07) as compared to the left (mean 2.61) side. The interaction of Group x Side was significant [F(2,87) = 6.78, P < 0.002]. Simple effect ANOVA of the interaction revealed that, whereas normal controls (right: mean 4.30; left: mean 2.43, P < 0.01) and heroin addicts (right: mean 4.40; left: mean 2.25, P < 0.01) exhibited a clear right-ward bias, alcoholics did not exhibit side-bias (right: mean 3.52; left: mean 3.16, P > 0.01).
Eyedness
Unlike limb lateralities, mixed factorial ANOVA with eye preference as the dependent measure yielded a significant main effect of Group [F(2,87) = 17.30, P < 0.001]. Normal controls (mean 3.67) had overall higher preference score followed by heroin addicts (mean 3.47) and alcoholics (mean 3.26). Eye bias was significantly more for the right (mean 4.12) than the left (mean 2.81) side [F(1,87) = 33.4, P < 0.001]. Post-hoc (simple effect ANOVA) analysis of the non-significant interaction of Group x Side indicated a clear rightward bias for normal controls (right: mean 4.340 left: mean3.00, P < 0.01) and heroin addicts (right: mean 4.40; left: mean 2.53, P < 0.01). Alcoholics (right: mean 3.61; left: mean 2.90, P > 0.01) did not exhibit any such bias (P > 0.01).
Earedness
Ear preference did not reveal a group difference; the main effect of Side was, however, significant indicating a right-ward bias (right: mean 4.24; left: mean 2.72) [F(1,87) = 88.9, P < 0.001]. The interaction of Group x Side was significant [F(2,87) = 28.45, P < 0.001]. As in other forms of side-bias, alcoholics exhibited atypical ear preference (right: mean 3.26, left: mean 3.45, P > 0.01). Heroin addicts (right: mean 4.80; left: mean 2.27, P < 0.01) and normal controls (right: mean 4.67, left: mean 2.45, P < 0.01) exhibited bias for the right side.
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DISCUSSION |
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Earlier findings on this issue documented a reduction of normal pattern of right handedness in alcoholics (Nasrallah et al., 1983; London, 1986
). McNamara et al. (1994) documented an increased prevalence of left handedness and learning disabilities in alcoholics. Earlier, Chyatte and Smith (1981) obtained a similar finding for alcoholics and speculated on the poor outcome of treatment for left-handed as compared to right-handed alcoholics (Smith and Chyatte, 1983
). These observations substantiate the prevalence of non-right handedness in alcoholics. In the present study, an identical pattern of observation was made for other forms of side-bias, such as footedness, eyedness, and earedness, in alcoholics. The associations amongst these behavioural measures in terms of preference were not found strong enough in normal subjects. In fact, preferential bias for long limbs (hand, foot) relative to sense organs (eye, ear) was observed as more consistent (Mandal et al., 1992a
). Interestingly, atypical (away from normal pattern of bias) side-bias has been found in this study to be a consistent feature across paired organs in alcoholics. This trend was reflected by a significant reduction in their rightward preference from other groups for all these forms of bias, thus supporting the notion of reduced pattern of lateralization in these subjects.
Because few explanations have been put forward as to why alcoholics exhibit such a pattern, it may be premature to draw conclusions. One may speculate that alcohol affects the dominant (left) hemisphere more adversely in comparison to the non-dominant (right) hemisphere which, in turn, affects the natural pattern of bias for the contralateral side. A second explanation entails a component of maturational/genetic defect (e.g. Geschwind and Galaburda, 1985). The view suggests that anomalous dominance (as a function of developmental delay, neuroimmune disorder, early cerebral insult, or genetic aberrations) may predispose individuals to alcoholism. Since side-bias is determined long before alcohol abuse begins, the latter explanation seems more suited to the present finding. Given such speculation, it may be interesting to observe in a future study the functional lateralization pattern in those who are at risk due to family history of developing alcoholism.
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FOOTNOTES |
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