Impaired conditional discrimination learning in schizophrenia
Introduction
Neuropsychological deficits have received growing attention in schizophrenia research (Brebion et al., 1997, Rund, 1998). The neuropsychological deficits found in schizophrenia with standardized test batteries have been heterogeneous. Individuals with schizophrenia showed impaired performance in functions such as abstraction, attention, language, memory and learning (Green and Walker, 1985, Braff et al., 1991, Saykin et al., 1991, Gruzelier et al., 1999). These impairments have been shown to be stable over time, implying that such dysfunctions could be trait markers of schizophrenia (Rosmark et al., 1999). Saykin has argued that memory and learning deficits might play a stronger role in the psychopathology and resulting impairment of patients with schizophrenia than other cognitive dysfunctions, and should be considered as more specific to schizophrenia than previously accepted.
Even though all researchers agree that neuro-psychological deficits exist, the relationship between neuropsychological deficits and specific regional brain functioning is to be treated with caution because of a multitude of methodologic problems (Keefe, 1995). Study results might depend on the present state of the subject, and almost all tasks used in neuropsychological tests are not specific to one brain region. Furthermore, it is difficult to control for the influence of a subject's motivation and attention on the test performance. Clearly, tests with a minimal requirement for active motivation should yield the most accurate results.
In the present study, we tried to avoid motivational influences by using an eyelid conditional discrimination learning (ECDL) task, which is an experimental method that places minimal demands on motivation and attention and in which the tested behavioral changes occur independently of conscious processes (Daum et al., 1991). ECDL is a well-established paradigm to investigate the ability to unconsciously develop differential responses to aversive versus non-aversive stimuli (Daum et al., 1991). ECDL has never been applied previously in schizophrenia studies.
In the ECDL paradigm, two behaviorally neutral stimuli (a red or a green light) are presented in random order. Only one of the stimuli (e.g. the green light) is followed by an aversive airpuff to the cornea after a fixed time interval. This is called a ‘reinforced trial’. In ‘unreinforced trails’ the light stimulus is not followed by an airpuff. The unpleasant aversive airpuff regularly elicits a reflex eye-blink. A conditioned response (CR) develops in healthy subjects after several trials. Eyelid closure then occurs already during presentation of the light stimulus. In other words, the subject unconsciously learns to avoid the aversive stimulus by closing the eyelid milliseconds before the airpuff onset. Healthy subjects show appropriate differential responding ability by developing significantly more CRs to the aversive reinforced as compared with unreinforced trials (Daum et al., 1991).
Thus ECDL is a task investigating implicit learning, a type of learning in which the subject receives no task-specific instruction and is unaware that she/he is acquiring a skill. This type of learning is considered to function differently from explicit learning, which is postulated to be a conscious process in modern concepts of memory and learning (Squire, 1987, Schacter, 1987). While other forms of learning have been repeatedly examined in schizophrenia (Saykin et al., 1991, Kosmidis et al., 1999), implicit learning has received little attention in the context of schizophrenia research (Schmand et al., 1992, Schwartz et al., 1992).
Section snippets
Aims and hypotheses
The aim of the study was to use ECDL to investigate the conditional discrimination avoidance learning ability of clinically stable individuals with schizophrenia and of healthy controls. We hypothesized that individuals with schizophrenia would show impaired performance in conditional discrimination avoidance learning compared with controls.
Subjects
Twenty-four consecutive patients with schizophrenia (SZ group) undergoing standard treatment at the outpatient unit of the Department of Psychiatry,
Subject variables
As shown in Table 1, there were no significant group differences regarding age and sex between patients and HCs. Moreover, there were no significant differences for age, sex, IQ, age at onset, duration of the disorder and PANSS scores between the paranoid and residual type patients. Subject variables were not considered for further analyses.
First occurrence of a conditioned response
All patients and HCs acquired CRs to the tone. Table 3 shows the median trial number of the occurrence of a FCR in the two groups and whether the FCR
Discussion
The major finding in this study is an impairment in conditioned aversive discrimination learning ability in clinically stable individuals with schizophrenia. At the beginning of the experiment (block 1), the patients showed only an insignificantly lower response rate compared with healthy controls.
During the course of the experiment conditioned response frequencies for both trial types stayed at the same level in the schizophrenic group (see Fig. 1). While the individuals with schizophrenia
Acknowledgements
This research was supported by grant No. 5657 ‘Jubiläumsfonds der Österr. Nationalbank’ (Austrian Federal Bank), Vienna, Austria to Karl Dantendorfer. We wish to thank Irene Daum, Bochum for her help in establishing the experimental setup and for invaluable comments on our work. We gratefully acknowledge the expert technical assistance of Markus Schugens, Bochum. We also acknowledge the important help in data acquistion and organization of Nicoletta Margreiter-Neuwirth and Maria Eberstaller.
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