Research report Aberrant brain dynamics in schizophrenia: delayed buildup and prolonged decay of the visual steady-state response Brett A. Clementz a, * , Andreas Keil b , Johanna Kissler b a Department of Psychology, University of Georgia, Psychology Building, Athens, GA 30602-3013, USA b Department of Psychology, Universita ¨t Konstanz, Constance, Germany Accepted 12 September 2003 Abstract In schizophrenia, aberrant brain activity has been reported both during stimulus processing and at rest. Evoked response amplitude is a function of both the number and synchronization of neurons firing in relation to a stimulus. It is at present unclear whether schizophrenia patients have normal synchronization of neural activity in relation to stimulus processing, and whether the amount and time course of synchronization is related to their evoked response amplitudes. EEG brain dynamics in response to visual steady-state stimulation were assessed in 12 schizophrenia and 12 healthy subjects at three stimulation durations (2, 4, and 6 s). Group differences in the visual evoked potential, the visual steady-state response, and the local coherence of the visual steady-state response were evaluated over time. Schizophrenia patients had smaller and delayed event-related potentials. Moreover, they had a slower buildup of steady-state amplitude following stimulation onset and a prolonged decrease after stimulation offset. Groups did not differ during mid-segments of steady-state stimulation. Increase in coherence to stimulation onset did not differ between-groups, but coherence decay of the visual steady-state response following stimulus offset was delayed in schizophrenia patients. The initial response to visual stimulation among schizophrenia subjects, therefore, may be reduced in amplitude due to weak signal strength, not poor coordination between distant cortical regions. The prolonged recovery function of schizophrenia patients’ visual system may indicate abnormal nonlinearity in neural response. These findings have implications understanding the nature of evoked response differences between schizophrenia and normal groups especially in repetitive stimulus paradigms. D 2003 Published by Elsevier B.V. Theme J: Disorders of the nervous system Topic: Neuropsychiatric disorders Keywords: Schizophrenia; Visual; Steady-state; Event-related potentials; Coherence 1. Introduction Studies of information processing in schizophrenia fre- quently rely on measures of event-related brain responses to transient stimuli. The predominant findings in these litera- tures are that schizophrenia patients have later and smaller event-related responses than do normal subjects [9,22,27,39]. The amplitude effect is especially prominent for lower frequency responses (in the theta and alpha ranges) after long (i.e. >3 s) inter-stimulus intervals [4,31,32]. The latency and magnitude of averaged event-related brain responses to transient stimuli are functions of both stimulus-evoked changes in phasic neural firing and stimu- lus-induced changes in background EEG activity [21,26]. First, presumably the more neurons are activated in response to a stimulus and/or the increased precision of their phase relationship the greater should be the evoked response power [11,33]. It is unknown how efficiently schizophrenia patients’ neural ensembles respond in relation to transient stimuli. It seems reasonable to suppose, however, that either excitatory drive on [10] and/or coordination between [2] neurons firing in relation to a transient stimulus is (are) suboptimal in schizophrenia. Second, there is an inverse relationship between the amount of pre-stimulus theta activity and magnitude of the slow wave components of transient event-related responses [1]. Schizophrenia patients have more low frequency EEG activity than normal both at rest [8] and during the course of stimulus presentation [38]. The possibility that differences in background brain activity, 0926-6410/$ - see front matter D 2003 Published by Elsevier B.V. doi:10.1016/j.cogbrainres.2003.09.007 * Corresponding author. Tel.: +1-706-542-4376; fax: +1-706-542- 3275. E-mail address: clementz@uga.edu (B.A. Clementz). www.elsevier.com/locate/cogbrainres Cognitive Brain Research 18 (2004) 121 – 129