Louis Kraft

Anterior Cingulate Metabolism Correlates with Stroop Errors in Paranoid Schizophrenia Patients

Using [O-15]-H2O PET Carter et al. (1997) reported that medicated patients with schizophrenia performing computerized single trial Stroop (1935) showed a reduction in the anterior cingulate activation response to the more attention demanding, incongruent Stroop condition. In that study, both patients and controls also showed a direct correlation between anterior cingulate activation and errors committed during incongruent trials of the task. In this study we follow up with an examination of paranoid schizophrenia outpatients and controls with very high resolution positron emission tomography (PET) and the longer half-life tracer [F-18]-fluorinated deoxyglucose (FDG) (Valk et al. 1990). All subjects (10 controls and 9 paranoid schizophrenia patients) were studied with FDG-PET while performing a computerized trial-by-trial version of the Stroop task during the uptake phase of the tracer (Carter et al. 1992). Results: As in previous studies using the single trial Stroop, patients were able to perform the task but made more color-naming errors during incongruent trials than controls. The patients in the present study showed a trend towards increased metabolic activity in the right anterior cingulate cortex. In the patient group, but not in controls, the anterior cingulate glucose metabolic rate correlated positively with the total incongruent trial errors. Conclusion: These results are consistent with the hypothesis that the anterior cingulate plays a performance-monitoring role during human cognition. This study does not rule out a reduction in error sensitivity in this region of the brain in schizophrenia, as other studies have suggested, however the data show that in unmedicated patients with the paranoid subtype this function is preserved to some extent.

Attentional control and word inhibition in schizophrenia

Previous studies have suggested that schizophrenia patients do not utilize contextual information efficiently to modulate attentional performance. The goal of the current study was to compare the utilization of context in modulating responses to irrelevant information on the Stroop task between a group of schizophrenia outpatients and matched controls. A single-trial version of the Stroop task was used to investigate performance on the Stroop task under three expectancy conditions. Eleven schizophrenia outpatients (on and off antipsychotic medication) and sixteen matched controls were tested. The schizophrenia patients showed: (1) augmented facilitation; (2) interference comparable to normals; and (3) normal ability to reduce interference under certain experimental circumstances. Schizophrenia patients were able to utilize contextual information under certain conditions and could modulate the magnitude of irrelevant word interference, although they were not able to overcome the prepotent tendency to read the word during the Stroop task as effectively as normals, which was reflected in greater Stroop facilitation. This suggests that the integrity or impairment of cognitive control functions in schizophrenia is related to the complexity of the context representation required to support that function.

The effects of antipsychotic medication on sequential inhibitory processes.

The authors used a Stroop negative priming paradigm to examine the effects of antipsychotic medication on selective attentional processes. The performance of 14 patients with schizophrenia who were withdrawn from neuroleptic medication was compared with that of 10 medicated patients and 16 matched controls. Results demonstrated an increase in negative priming to normal levels with neuroleptic therapy. In contrast, within-trial interference and facilitation effects appeared to be less sensitive to medication therapy. The sustainment of inhibitory processes over time may differentiate the inhibitory mechanisms of the medication-withdrawn patients from both the medicated patients and the matched controls. The study of sequential inhibitory processes and their response to neuroleptic treatment could be important methods for understanding the temporal parameters associated with inhibition in schizophrenia.

Effect of movement on human spinal and subcortical somatosensory evoked potentials

Sensory transmission in dorsal column nuclei is inhibited during voluntary movement in experimental animals. We have studied the human response by recording spine and scalp somatosensory evoked potentials. Finger movement attenuated the amplitude and duration of the cervical N13 and the scalp N18 and N20 waves. Foot movement did not alter the lumbar N22 after foot stimulation, but the scalp P38 was attenuated. N22 results solely from activation of interneurons in the dorsal gray of the cord at the root entry zone, but N13 may receive contributions from the nucleus cuneatus. Therefore, the movement-induced attenuation of N13 is attributed to decreased contribution from the nucleus cuneatus.

Cervical synapse-dependent somatosensory evoked potential following posterior tibial nerve stimulation

We have demonstrated the presence of a localized, synapse-dependent negativity (N29) recorded over the upper cervical spine after bilateral stimulation of the posterior tibial nerves at the ankle. The amplitude of N29 is maximal at the level of the second cervical spine and decreases at more rostral and caudal levels. The peak latency of N29 remains constant at all levels. N29 has a long refractory period when compared with the refractory period of the afferent volley recorded at either the sacral or thoracic level. N29 is most likely generated by activation of the nucleus gracilis by the afferent volley. The cervical N13 after median nerve stimulation probably has multiple generator sites, including the nucleus cuneatus.