Magnetic resonance imaging and single photon emission tomography in treatment-responsive and treatment-resistant schizophrenia.

BACKGROUND: Patients with schizophrenia differ from controls in several measures of brain structure and function, but it is uncertain how these relate to clinical features of the illness. We dichotomised patient groups by treatment response to test the hypothesis that treatment-resistant patients exhibit more marked biological abnormalities than treatment-responsive patients. METHOD: Twenty treatment-responsive and 20 treatment-resistant patients with schizophrenia, matched for sex, age, and illness duration, were compared by magnetic resonance imaging, single photon emission tomography, and detailed neuropsychological assessment. RESULTS: Brain-imaging variables were not statistically related to treatment response, although poorly responsive patients had lower volumes of most brain structures. Several highly significant differences emerged between patient groups on neuropsychological testing. Episodic memory functioning distinguished patient groups even after we controlled for global cognitive impairment. CONCLUSIONS: Cerebral structure and blood flow have a limited effect on treatment response in schizophrenia, but long-term episodic memory impairment is associated with, and may predict, poor prognosis

Modelling assimilation rates of 14 temperate arable weed species as a function of the environment and leaf traits

Information on the response of assimilation rate to environmental factors is lacking for many less competitive weed species that need to be considered in the context of increasing farm biodiversity. A pot experiment was sown to parameterize gross assimilation rate at light saturation and initial light use efficiency for 14 common UK annual weeds and winter wheat at four leaf temperatures. Field experiments were also sown to measure inter-specific differences in specific leaf area (SLA), leaf nitrogen content and assimilation rates in the field at near-optimum temperatures. A generic relationship describing the response of assimilation rate to temperature and light using SLA and leaf nitrogen content as conversion factors successfully predicted inter-specific differences in assimilation rates in the field. This relationship could be incorporated into weed-crop competition models to predict the productivity and competitive impact of weed mixtures, including species outside the current data set. Assimilation rates at light saturation in the field were determined largely by SLA. This trait was variable between species and within a species across the growing season and needs to be well described in mechanistic competition models to accurately calculate instantaneous assimilation rates.Peer reviewe