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BIOL PSYCHIATRY 1991 ;29:900-908

Cerebral Laterality, Perception of Emotion, and Treatment Response in Obsessive-Compulsive Disorder Bruce E. Wexler and Wayne K. Goodman

Patients with obsessive--compulsive disorder (OCD) had lower right-ear advantages than healthy controls on five different language-related dichotic listening tests of cerebral lateralit3'. This abnormality was more pronounced in patients with more severe illness. Stimulus pairs in one test consisted of one word with a positive emotional valence and one emotionally neutral word. Pairs in another test consisted of one negative and one neutral word. Patients with OCD tended to hear fewer emotion-related words than did healthy controls, a finding also noted in depressed patients. Moreover, OCD patients who responded to treatment with serotonin reuptake inhibitors heard fewer emotionrelated words than did nonresponders.

Introduction Growing appreciation of the prevalence of obsessive--compulsive disorder (OCD) has led to increased interest in its neurobiology. Several studies suggest the possibility of lateralized left-hemisphere (LH) abnormalities, including increased metabolic activity (Baxter et al 1987), blood flow (Zohar et al 1989), evoked potential amplitude (Shagass et al 1984; Towey et al 1990) and electroencephalographic (EEG) power (Flor-Henry et al 1979). However, two immediate problems limit efforts to interpret these initial findings. First, follow-up studies failed to find consistently lateralized increases in metabolic activity, thereby raising questions about both this finding and those for which replications have not yet been attempted (Baxter et ai 1988; Nordahl et al 1989). Second, even if the lateralized abnormalities in metabolic and electrical activity exist, it is not possible from existing studies to know whether the changes mark increased or decreased LH function, although some investigators have speculated that the former may be the case (Towey et al 1990). In the present study we used language-related dichotic listening tests to investigate further the possibility of lateralized alteration in brain function of OCD patients. In dichotic listening tests, two different stimuli are presented simultaneously, one to each ear. Studies of postcommissurotomy patients show that if there is sufficient temporal and auditory spectral overlap between the members of each dichotic stimulus pair, information from From the Department of Psychiatry, Clinical Neuroscience Research Unit (WKG), Yale University and the Connecticut Menial Health Cen!er (BEWL New Haven, CT. Address reprint requests to Dr. Bruce E. Wexler, Connecticut Mental Health Center, 34 Park St., New Haven, CT 06519. Received October 19, 1990; revised December 7, 1990. © 1991 Society of Biological Psychiatry

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Laterality and Emotion in OCD

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Table !. The Five Dichotic Tests, the Dependent Measures Resulting From Them, and t ~ Possible Comparisons Between Each Test and Previous Studies Dependent measures Dichotic tests

Laterality (REA)

Nonsense syllables Words Neutral-Neutral words Positive-Neutral words Negative-Neutral words

X X X X X

Perception of emotion (EPI)

X X

Possible c o m p a ~ Rapoport study

Dept'essed patients

Schizophrenic l:~_tients

X

X X X X X

X X

the minor ipsilateral auditory afferent pathways is lost, and subjects respond only on the basis of information carried by the contralateral pathways (Sparks and Geschwind 1968; Milner et al 1968; Springer 1978). This has recently beea confirmed in patients given a language-related dichotic listening test while under conditions of single hemisphere narcosis from unilateral carotid artery injection of barbiturate. These indifiduals could report any of the words presented to their left ears while their right hemispheres ( ~ ) were anesthetized (Michel et al 1986). Thus, in dichotic tests information from each ear is processed initially in the contralateral cerebral hemisphere. When the dichotic pairs consist of language-related stimuli, there is usually a perceptual advantage for information presented to the right ear. This results from the fact that information from the right ear goes directly to the LH, which is usually the hemisphere specialized for l a n ~ a g e processing, while information from the left ear goes first to the RH and must then be transferred across to the LH (Studdert-Kennedy 1975; Wexler 1988). Changes in LH or RH function, or in interhemispheric information flow, can be detected in alterations in the magnitude of this right-ear advantage (REA). Rapoport and colleagues (Rapoport et al 1981; Ludlow et al 1989) reported a significant decrease in REA on a dichotic nonsense syllables test in adolescents with OCD. This finding would suggest that subsequent findings of possible LH abnormalities in metabolic and electrical activity were markers of decreased rather than h'icreased LH function. The present study sought to replicate and extend the finding of Rapoport et al, using a battery of five different dichotic tests in a group of 22 adult OCD patients (Table I). The two stimuli in each stimulus pair (in all tests) differed from one another in opAy a single consonant. Computer speech generation and cross-splicing techniques were used to construct stimulus pairs that were in fact identical save for the single distinguishing consonant. The resulting high degree of auditory spectral overlap causes the two stimuli in each pair to fuse into a single auditory percept, and subjects are aware of heating only one stimulus on each trial. These fused single-response tests have proved highly reliable with testretest correlations of REA scores of 0.88 to 0.90 (Wexler et al 1981; Wexler and Halwes 1983). Neurologic validity has been supported by finding that the proportions of rightand left-handed subjects with right- and left-ear advantages match the proportions of each group thought to have LH or RH language specialization (Wexler and Halwes 1983). More direct support for the neurclogic validity of the fused dichotic tests is provided by a recent subject-by-subject comparison of hemispheric specialization for speech as determined by intracarotid amytal in iection and direction of ear advantage (Zatorre 1989). Pairs in one of the dichotic tests consisted of one word with a positiw: emotional

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BIOL PSYCHIATRY 1991;29:900-908

B.E. Wexler and W.K. Goodman

valence and one emotionally neutral word (e.g., fun-ton). Pairs in another test consisted of a negative and a neutral word (e.g., kill-fill). Because the two words in each stimulus pair fuse into a single auditory percept, and subjects are consciously aware of hearing only one word on each trial, it is also possible to determine whether patients differ from controls in the proportion of times they hear the emotion-evoking word as opposed to the neutral word. Recent studies have found that depressed patients hear fewer positive and fewer negative words than do controls [Wexler et al (1991) unpublished article], and that healthy women hear fewer positive words premenstmally than postmenstrually (AIremus et al 1989a).

Experimental Method Subjects Twenty-two patients (10 men, 12 women) with a principal diagnosis of OCD based on a structured interview applying DSM-IH-R criteria, and enrolled in inpatient (n = 7) or outpatient treatment programs on the Clinical Neuroscience Research Unit at the Connecticut Mental Health Center participated. All were drug free for at least 4 weeks at the time of testing. The group mean Yale-Brown Obsessive Compulsive Scale (Y-BOCS) (Goodman et al 1989) score was 23.9 with a range of 9-39. Ten patients had 24-item Hamilton Depression ratings >20, 6 had ratings ~>15 and

Cerebral laterality, perception of emotion, and treatment response in obsessive-compulsive disorder.

Patients with obsessive-compulsive disorder (OCD) had lower right-ear advantages than healthy controls on five different language-related dichotic lis...
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