UNLABELLED: Mild hypothermia may be induced during neurosurgery for brain protection. However, its effect on propofol requirement has not been defined. Accordingly, we tested the hypothesis that 3 degrees C of core hypothermia decreases the propofol blood concentration at which patients respond to command (CP50-awake) in neurosurgical patients. Forty patients were anesthetized with alfentanil 50 microg/kg i.v., nitrous oxide, propofol target-controlled infusion, and rocuronium. The bispectral index (version 3.12) was monitored continuously. Patients were randomized to a core temperature of 34 degrees C or 37 degrees C. At the end of surgery, neuromuscular blockade was reversed, nitrous oxide was ceased, and propofol was infused to achieve a blood target determined by the previous patient's response. Responsiveness to command was assessed 15 min later. Results were analyzed with logistic regression models; P < 0.05 was considered statistically significant. The CP50-awake of propofol was 3.05 microg/mL (95% confidence interval, 2.34-3.66). Propofol concentration, but not core temperature, predicted loss of response to command (odds ratio, 11.76; 95% confidence interval, 2.40-57.63; P < 0.01). Core temperature did not alter the relationship between bispectral index and response to command. Propofol infusion regimens may not require adjustment during mild hypothermia. IMPLICATIONS: Neurosurgical patients may be allowed to become mildly hypothermic during anesthesia in an effort to provide brain protection. Propofol maintenance infusion doses may not require adjustment in these patients.

Adult↗

PubMed2002

Shape constancy in autism: the role of prior knowledge and perspective cues.

BACKGROUND: Evidence suggests that individuals with autism may not attend to contextual information (conceptual or perceptual) when processing stimuli (Frith 1989; Shah & Frith, 1983). METHOD: We investigated the role of prior knowledge and perspective cues when judging the shape of a slanted circle in individuals with and without autism. Individuals adjusted a shape on a computer screen to appear the same as a slanted circle. RESULTS: Participants in all groups (autistic, moderate learning difficulties, children aged 9 years and adults) exaggerated circularity. Strikingly, however, individuals with autism were unique in exaggerating circularity significantly far less when perspective cues surrounding the slanted circle were eliminated. Prior knowledge that the shape was a slanted circle provoked a strong exaggeration effect in participants without autism, but not in those with autism. CONCLUSIONS: Perhaps classifying the stimulus as a 'circle' was sufficient to provoke a strong exaggeration effect in those without (but not with) autism. In this domain, we show that perception in autism may be less influenced by prior knowledge, and therefore less 'top-down'.

Adolescent↗

PubMed1999