Aversive gustatory stimulation activates limbic circuits in humans

Animal studies implicate the amygdala and its connections in the recognition of aversive stimuli. A recent PET study demonstrated that the human amygdala and left orbitofrontal cortex show substantial increases in regional cerebral blood flow (rCBF) during exposure to aversive odourants. To examine if aversive gustatory stimuli similarly activate these regions, nine healthy women tasted an aversive saline solution, pure water and chocolate while rCBF was measured with PET. The aversive saline condition, when contrasted with the water condition, increased activity in the right amygdala, left anterior orbitofrontal cortex, medial thalamus, pregenual and dorsal anterior cingulate, and the right hippocampus. The right amygdala, left orbitofrontal cortex and pregenual cingulate remained significantly activated when saline was compared with chocolate. The present results indicate that the amygdala and orbitofrontal cortex respond to aversive stimuli in both the olfactory and gustatory modalities, and highlight the role of the pregenual cingulate in negative emotional processing.

Emotion, olfaction, and the human amygdala: amygdala activation during aversive olfactory stimulation

Electrophysiologic and lesion studies of animals increasingly implicate the amygdala in aspects of emotional processing. Yet, the functions of the human amygdala remain poorly understood. To examine the contributions of the amygdala and other limbic and paralimbic regions to emotional processing, we exposed healthy subjects to aversive olfactory stimuli while measuring regional cerebral blood flow (rCBF) with positron emission tomography. Exposure to a highly aversive odorant produced strong rCBF increases in both amygdalae and in the left orbitofrontal cortex. Exposure to less aversive odorants produced rCBF increases in the orbitofrontal cortex but not in the amygdala. Change of rCBF within the left amygdala and the left OFC was highly intercorrelated, indicating a strong functional interaction between these brain regions. Furthermore, the activity within the left amygdala was associated significantly with subjective ratings of perceived aversiveness. These findings provide evidence that the human amygdala participates in the hedonic or emotional processing of olfactory stimuli.

Anatomy and function of the orbital frontal cortex, I: anatomy, neurocircuitry; and obsessive-compulsive disorder

Many neuroimaging studies have implicated the orbital frontal cortex (OFC) in the pathophysiology of obsessive-compulsive disorder. In recent years there have been significant advances in elucidating the anatomical characteristics of the OFC in nonhuman primates. The authors review literature on the cytoarchitecture and afferent and efferent connections of the OFC, giving particular attention to the OFC's relationship to limbic and paralimbic regions, the mediodorsal thalamus, the basal ganglia, and sensory association cortices. These cytoarchitectural divisions and connections are discussed in terms of how they may influence thinking about the OFC's contribution to obsessive-compulsive disorder.

Anatomy and function of the orbital frontal cortex, II: Function and relevance to obsessive-compulsive disorder

The authors review neurophysiological, neurobehavioral, and neuropsychological investigations of the orbital frontal cortex (OFC) in human and non-human primates. The article critically examines the role of the OFC in 1) recognition of reinforcers; 2) stimulus-reinforcer learning; 3) modulation of responses based on changes in reinforcement contingencies; 4) emotions, social behavior, and autonomic regulation; 5) mnemonic functions; and 6) rule learning. Examining these functional areas with reference to the OFC's anatomical and neurophysiological properties, the authors suggest ways in which the OFC might contribute to obsessive-compulsive disorder.

The D5 dopamine receptor gene in schizophrenia: identification of a nonsense change and multiple missense changes but lack of association with disease

To determine whether mutations in the D5 dopamine receptor gene (DRD5) are associated with schizophrenia, the gene was examined in 78 unrelated schizophrenic individuals (156 DRD5 alleles). After amplification by the polymerase chain reaction, products were examined by dideoxy fingerprinting (ddF), a screening method related to single strand conformational polymorphism analysis that detects essentially 100% of mutations. All samples with abnormal ddF patterns were sequenced. Nine different sequence changes were identified. Five of these were sequence changes that would result in protein alterations; of these, one was a nonsense change (C335X), one was a missense change in an amino acid conserved in all dopamine receptors (N351D), two were missense changes in amino acids that are identical in only some dopamine receptors and in only some species (A269V; S453C), and one was a missense change in a non-conserved amino acid (P330Q). To investigate whether the nonsense change (C335X), predicted to prematurely truncate the receptor protein and result in a 50% diminution of functional protein, was associated with schizophrenia, other neuropsychiatric diseases, or specific neuropsychological, psychophysiological, or personality traits, both case-control and family analyses were performed. No statistically-significant associations were detected with schizophrenia or other neuropsychiatric disease. There also were no significant associations between any one measure of neuropsychological function. However, a post-hoc analysis of combined measures of frontal lobe function hinted that heterozygotes for C335X may have a vulnerability to mild impairment, but these findings must be interpreted with caution.(ABSTRACT TRUNCATED AT 250 WORDS)