Pathological Imitative Behavior and Response Preparation in Schizophrenia.

INTRODUCTION: Pathological imitative behavior (ehopraxia) is occasionally observed in schizophrenia patients. However, only a severe form of echopraxia can be detected with the help of a direct observation. Therefore, our goal was to study a latent form of pathological imitative behavior in this disorder, which is indicated by an increase of imitative tendencies. METHOD: In our study, 14 schizophrenia patients and 15 healthy subjects were employed in two tasks: (a) in an imitative task they had to copy a hand action seen on a screen; (b) in a counter-imitative task they had to make a different movement (which involves an inhibition of prepotent imitative tendency that is impaired in case of pathological imitative behavior). Imitative tendencies were assessed by an interference score - a difference between counter-imitative and imitative response parameters. We also studied a response preparation in both groups by employing precueing probabilistic information. RESULTS: Our results revealed that schizophrenia patients were able to employ probabilistic information to prepare properly not only the imitative, but also the counter-imitative responses, the same as the healthy subjects did. Nevertheless, we detected increased prepotent imitative tendencies in schizophrenia patients, what indicates the latent pathological imitative behavior in case of this disorder. CONCLUSIONS: The obtained results suggest that in the case of schizophrenia problems with pathological imitative behavior more likely occurred in executive rather than in the preparatory stage of response. Our findings can help to detect a latent echopraxia in schizophrenia patients that cannot be revealed by direct observation.

Response preparation and intra-individual reaction time variability in schizophrenia.

Background. It is important to prepare response in advance to increase the efficiency of its execution. The process of response preparation is usually studied using the precueing paradigm. In this paradigm subjects have to employ the preceding information about further imperative stimulus to perform proper response preparation, which shortens the reaction time of subsequent response execution. Previous studies detected the impairment of response preparation in schizophrenia only with the help of electroencephalographic parameters, but not with the assessing of reaction time. Therefore, in this study we attempted to find a behavioural parameter that could detect impairment in response preparation of schizophrenia patients. It was recently found that appropriate response preparation not only shortens the reaction time but also increases its stability, which is measured with the intra-individual reaction time variability. It was also revealed that response stability could better find cognitive dysfunction in some studies of schizophrenia disorder than classical behavioural parameters. Hence, the main goal of this study was to verify if intra-individual reaction time variability could detect the impairment of response preparation in schizophrenia patients. Materials and methods. In order to achieve the main purpose, we carried out a study with 14 schizophrenia patients and 14 control group subjects. We used precueing paradigm in our research, in which participants had to employ information about stimulus probability for the proper response preparation. Results. Our main result showed that despite the responses of schizophrenia patients were faster to the high-probability stimulus than to the low-probability one (F (1, 13) = 30.9, p < 0.001), intra-individual reaction time variability did not differ in this group between the responses to more and less probable stimuli (F (1, 13) = 0.64, p = 0.44). Conclusions. Results of the study suggest that people with schizophrenia were able to use precueing probabilistic information only to shorten their reaction time, but not to increase response stability. Therefore, it was found that intra-individual reaction time variability parameter could detect response preparation impairment in schizophrenia, and could be used in clinical purposes.

Intra-individual reaction time variability and response preparation: an EEG study.

To behave more efficiently the human brain must anticipate future events with different probabilities and prepare appropriate responses. Previous studies demonstrated that participants react faster to more probable stimuli. It has been shown that this effect in reaction time reduction is related to the response preparation process. However it is still unknown what the minimum difference in stimulus probabilities is that is sufficient to elicit response preparation as measured with the EEG. Intra-individual reaction time variability indicates the stability of an individual's response performance and provides useful information about cognitive functioning. It's use has become prevalent in recent clinical studies. In order to extend understanding of cognitive and neural mechanisms of response stability we hypothesized that intra-individual reaction time variability relates to the response preparation process. Specifically, we hypothesized that response preparation to more probable stimuli would result in not only faster reaction time but also in a reduction of response variability. To verify this hypothesis, we tested 14 healthy subjects using reaction time and EEG as dependent measures. Two different stimuli with probabilities of 33.3% and 66.6% were assigned to two counterbalanced responses. The results of our study showed that stimulus probabilities of 66.6% and 33.3% were sufficient to elicit response preparation. Our data also revealed that response preparation to more probable stimuli speeds RT and reduces RT variability.