RationaleMany studies have reported deficits of mismatch negativity (MMN) in schizophrenic patients. Pharmacological challenges with hallucinogens in healthy humans are used as models for psychotic states. Previous studies reported a significant reduction of MMN after ketamine (N-methyl-D-aspartate acid [NMDA] antagonist model) but not after psilocybin (5HT2...
The psychosis associated with schizophrenia is characterized by alterations in sensory processing and perception. Some antipsychotic drugs were identified by their high affinity for serotonin 5-HT2A receptors (2AR). Drugs that interact with metabotropic glutamate receptors (mGluR) also have potential for the treatment of schizophrenia. The effects of halluci...
RationaleBinocular rivalry occurs when different images are simultaneously presented to each eye. During continual viewing of this stimulus, the observer will experience repeated switches between visual awareness of the two images. Previous studies have suggested that a slow rate of perceptual switching may be associated with clinical and drug-induced psycho...
Patients with schizophrenia exhibit diminished prepulse inhibition (PPI) of the acoustic startle reflex and deficits in the attentional modulation of PPI. Pharmacological challenges with hallucinogens are used as models for psychosis in both humans and animals. Remarkably, in contrast to the findings in schizophrenic patients and in animal hallucinogen model...
IntroductionPharmacological challenges with hallucinogens are used as models for psychosis in experimental research. The state induced by glutamate antagonists such as phencyclidine (PCP) is often considered as a more appropriate model of psychosis than the state induced by serotonergic hallucinogens such as lysergic acid diethylamide (LSD), psilocybin and N...
Binocular rivalry occurs when different images are presented simultaneously to corresponding points within the left and right eyes. Under these conditions, the observer's perception will alternate between the two perceptual alternatives. Motivated by the reported link between the rate of perceptual alternations, symptoms of psychosis and an incidental observ...
We report results of a FDG-PET study in 10 patients with schizophrenia (6 unmedicated, 4 never medicated) and 12 healthy age-matched controls. The patients met ICD-10 and DSM-IV criteria for schizophrenia and all reported psychotic, "positive" symptoms when tested. Schizophrenic patients had higher absolute CMRGlu values in almost all quantified regions comp...
The hallucinogenic serotonin(1A&2A) agonist psilocybin is known for its ability to induce illusions of motion in otherwise stationary objects or textured surfaces. This study investigated the effect of psilocybin on local and global motion processing in nine human volunteers. Using a forced choice direction of motion discrimination task we show that psilocyb...
ObjectiveThis paper describes two cases with khat- and two with psilocybin-induced psychoses and draws attention to the medical and social consequences of the use of these drugs.MethodTwo male patients are presented who developed relapsing and short-lasting psychotic episodes after chewing kath leaves. In addition, two male patients are reported who showed a...
Increasing evidence from neuroimaging and behavioral studies suggests that functional disturbances within cortico-striato-thalamic pathways are critical to psychotic symptom formation in drug-induced and possibly also naturally occurring psychoses. Recent basic and clinical research with psychotomimetic drugs, such as the N-methyl-D-aspartate (NMDA) glutamat...
The modulating effects of serotonin on dopamine neurotransmission are not well understood, particularly in acute psychotic states. Positron emission tomography was used to examine the effect of psilocybin on the in vivo binding of [11C]raclopride to D2-dopamine receptors in the striatum in healthy volunteers after placebo and a psychotomimetic dose of psiloc...
Psilocybin, an indoleamine hallucinogen, produces a psychosis-like syndrome in humans that resembles first episodes of schizophrenia. In healthy human volunteers, the psychotomimetic effects of psilocybin were blocked dose-dependently by the serotonin-2A antagonist ketanserin or the atypical antipsychotic risperidone, but were increased by the dopamine antag...
The effects of the indolehallucinogen psilocybin, a mixed 5-HT2 and 5-HT1 agonist, on regional cerebral glucose metabolism were investigated in 10 healthy volunteers with PET and [F-18]-fluorodeoxyglucose (FDG) prior to and following a 15- or 20-mg dose of psilocybin. Psychotomimetic doses of psilocybin were found to produce a global increase in cerebral met...
Hallucinogenic drugs (psychedelics, e.g. Psilocybin, Mescaline, LSD) induce in humans qualitatively altered states of consciousness (ASC), which can be used as experimental models for endogenous psychosis. However, some researchers claim that these ASCs are not appropriate models for schizophrenia. We report two clinical cases of acute endogenous psychoses d...
Hallucinogenic drugs are unique in that they produce the desired hallucinogenic effects at what are considered non-toxic doses. The hallucinogenic drugs can be categorised into 4 basic groups: indole alkaloid derivatives, piperidine derivatives, phenylethylamines and the cannabinols. The drugs reviewed include lysergic acid diethylamide (LSD), phencyclidine ...
Psychotic states are mimicked by the use of many drugs including amphetamines, cannabis, lysergic acid diethylamide, psilocybin, mescaline, isoniazid, and L-dopa. A paranoid psychotic picture in a clear sensorium is characteristic of amphetamine psychosis. In developing countries, malaria among other diseases is a frequent indicator of chloroquine administra...
A radioimmunoassay procedure has been developed to monitor patients suspected of phencyclidine (PCP) intoxication. Symptoms in 11 patients suspected of phencyclidine intoxication included violent, aggressive behavior with delusions, hallucinations, agitation, and other signs of toxic psychosis. In five subjects serum concentrations of PCP ranged between 0.5 ...
The effects of the psilocybin, a psychomimetic substance, on mental junctioning were investigated in normal volunteers as well as in schizophrenics. The disturbances induced constitute a psychoneurotoxic syndrome--"a state of drunkenness"--of about four hours duration which develops in three distinct phases. The basic mental symptoms of this syndrome consist...
