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Top-down attentional modulation of primary auditory cortex in schizophrenia
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PSYCHIATRY
TOP-DOWN ATTENTIONAL MODULATION OF PRIMARY AUDITORY CORTEX IN SCHIZOPHRENIA Nick Ramsey*, Nienke van Atteveldtt,
Wiepke CahnS, R.S. Kahn*
*Functional Neuroimaging Section, Dept. Psychiatry, University Medical Center Utrecht, Netherlands tDept. Psychology, University of Maastricht, Netherlands *Dept. Psychiatry, University Medical Center Utrecht, Netherlands Background Schizophmnic patients generally exhibit deficits in discriminating relevant from irrelevant stimuli when these compete for attention. In healthy subjects, attention to specific stimulus features has been shown to enhance brain activity in the primary cortex of the attended modality. Activity in the cortex of non-attended modalities is a the same time reduced, suggesting that attention involves top-down regulation of stimulus processing at an early level (1). The reduced capacity to focus attention observed in schizophrenic patients may be a consequence of ineffective top-down regulation of primary cortex activity, resulting in competition of relevant and irrelevant information at higher levels of cognitive processing (2). To address this hypothesis we conducted an fMRJ study with 8 schizophrenic patients treated with atypical neuroleptics and 9 healthy controls. Methods Subjects had to pay attention either to visual or to auditory stimuli which were presented simultaneously, by detecting stimuli with a slightly different size (visual) or frequency (auditory). Task difficulty, i.e. size and frequency contrast, was adjusted for each subject so that all made approximately 80 % correct responses. This was done to obtain an equal load on the attentional system for both groups. Larger contrasts were required for patients, indicating reduced capacity to discriminate stimuli within the same modality. Brain activity was examined in auditory cortex and in frontal regions associated with attentional processing (anterior cingulate and Activity in Auditory Cortex (Al-A21 dorsolateral prefrontal cortex). ReSttlts We found that the auditory cortex was clearly modulated by attentional demand (i.e. aimed at auditory versus visual stimuli), in that the activity that was invoked by auditory stimuli,was reduced when paying attention to visual stimuli. Patients exhibited the same degree of attentional modulation of auditory cortex as controls. Activity in the frontal regions was present during both conditions, but did not vary with attentional demand. Activity in dorsolateral prefrontal cortex was decreased in patients, regardless of demand. Anterior cingulate cortex was active, during both conditions, in both groups, and was not affected by attentional demand.
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ContrdS Patients conclusions We conclude that in schizophrenic patients the attentional modulation of auditory primary cortex appears to be normal, and that reduced activity in prefrontal cortex may underlie the reduced capacity to discriminate stimuli in terms of size (visual modality) and frequency (auditory modality). References 1 Rees, G., Frith, C. D., 6’~Lavie, N. 1997, Modulating irrelevant motion perception by varying attentional load in an unrelated task, Science, vol. 278,110.5343, pp. 1616-1619. 2 Mcctie A, Chapman, J, 1961, Disorders of attention and perception in early schizophrenia. BR.J.Med.Psychol. 34:103-116
s1092
13, r4umLle.r
0, ‘UUI,
ran
L or ‘ ram
IllEjp-
PSYCHIATRY
TOP-DOWN ATTENTIONAL MODULATION OF PRIMARY AUDITORY CORTEX IN SCHIZOPHRENIA Nick Ramsey*, Nienke van Atteveldtt,
Wiepke CahnS, R.S. Kahn*
*Functional Neuroimaging Section, Dept. Psychiatry, University Medical Center Utrecht, Netherlands tDept. Psychology, University of Maastricht, Netherlands *Dept. Psychiatry, University Medical Center Utrecht, Netherlands Background Schizophmnic patients generally exhibit deficits in discriminating relevant from irrelevant stimuli when these compete for attention. In healthy subjects, attention to specific stimulus features has been shown to enhance brain activity in the primary cortex of the attended modality. Activity in the cortex of non-attended modalities is a the same time reduced, suggesting that attention involves top-down regulation of stimulus processing at an early level (1). The reduced capacity to focus attention observed in schizophrenic patients may be a consequence of ineffective top-down regulation of primary cortex activity, resulting in competition of relevant and irrelevant information at higher levels of cognitive processing (2). To address this hypothesis we conducted an fMRJ study with 8 schizophrenic patients treated with atypical neuroleptics and 9 healthy controls. Methods Subjects had to pay attention either to visual or to auditory stimuli which were presented simultaneously, by detecting stimuli with a slightly different size (visual) or frequency (auditory). Task difficulty, i.e. size and frequency contrast, was adjusted for each subject so that all made approximately 80 % correct responses. This was done to obtain an equal load on the attentional system for both groups. Larger contrasts were required for patients, indicating reduced capacity to discriminate stimuli within the same modality. Brain activity was examined in auditory cortex and in frontal regions associated with attentional processing (anterior cingulate and Activity in Auditory Cortex (Al-A21 dorsolateral prefrontal cortex). ReSttlts We found that the auditory cortex was clearly modulated by attentional demand (i.e. aimed at auditory versus visual stimuli), in that the activity that was invoked by auditory stimuli,was reduced when paying attention to visual stimuli. Patients exhibited the same degree of attentional modulation of auditory cortex as controls. Activity in the frontal regions was present during both conditions, but did not vary with attentional demand. Activity in dorsolateral prefrontal cortex was decreased in patients, regardless of demand. Anterior cingulate cortex was active, during both conditions, in both groups, and was not affected by attentional demand.
120
WXknd blsud ~&tend AudItot
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,100 ;
80
g 80 640 2 20
0
ContrdS Patients conclusions We conclude that in schizophrenic patients the attentional modulation of auditory primary cortex appears to be normal, and that reduced activity in prefrontal cortex may underlie the reduced capacity to discriminate stimuli in terms of size (visual modality) and frequency (auditory modality). References 1 Rees, G., Frith, C. D., 6’~Lavie, N. 1997, Modulating irrelevant motion perception by varying attentional load in an unrelated task, Science, vol. 278,110.5343, pp. 1616-1619. 2 Mcctie A, Chapman, J, 1961, Disorders of attention and perception in early schizophrenia. BR.J.Med.Psychol. 34:103-116
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