Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal. The claustrum, a region whose function had been unclear, displayed one of the highest activations. Additionally, activations were recorded in paralimbic areas (anterior cingulate gyrus, orbitofrontal cortex), in the striatum (head of caudate nucleus, putamen), and in the posterior hypothalamus. By contrast, decreased rCBF was observed in several temporal areas. Based on these results, we propose a model of the brain processes mediating the cognitive, emotional, motivational, and autonomic components of human male sexual arousal. Hum. Brain Mapping 11:162–177, 2000. © 2000 Wiley‐Liss, Inc.

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The functional anatomy of perceptual and semantic processings for odors was studied using positron emission tomography (PET). The first experiment was a pretest in which 71 normal subjects were asked to rate 185 odorants in terms of intensity, familiarity, hedonicity, and comestibility and to name the odorants. This pretest was necessary to select the most appropriate stimuli for the different cognitive tasks of the second experiment. The second one was a PET experiment in which 15 normal subjects were scanned using the water bolus method to measure regional cerebral blood flow (rCBF) during the performance in three conditions. In the first (perceptual) condition, subjects were asked to judge whether an odor was familiar or not. In the second (semantic) condition, subjects had to decide whether an odor corresponded to a comestible item or not. In the third (detection) condition, subjects had to judge whether the perceived stimulus was made of an odor or was just air. It was hypothetized that the three tasks were hierarchically organized from a superficial detection level to a deep semantic level. Odorants were presented with an air-flow olfactometer, which allowed the stimulations to be synchronized with breathing. Subtraction of activation images obtained between familiarity and control judgments revealed that familiarity judgments were mainly associated with the activity of the right orbito-frontal area, the subcallosal gyrus, the left inferior frontal gyrus, the left superior frontal gyrus, and the anterior cingulate (Brodmann's areas 11, 25, 47, 9, and 32, respectively). The comestibility minus familiarity comparison showed that comestibility judgments selectively activated the primary visual areas. In contrast, a decrease in rCBF was observed in these same visual areas for familiarity judgments and in the orbito-frontal area for comestibility judgments. These results suggest that orbito-frontal and visual regions interact in odor processing in a complementary way, depending on the task requirements.

The clinical, electrophysiological and haemodynamic effects of precentral gyrus stimulation (PGS) as a treatment of refractory post-stroke pain were studied in 2 patients. The first patient had a right hemibody pain secondary to a left parietal infarct sparing the thalamus, while the second patient had left lower limb pain developed after a right mesencephalic infarct. In both cases, spontaneous pain was associated with hyperpathia, allodynia and hypoaesthesia in the painful territory involving both lemniscal and extra-lemniscal sensory modalities in patient 1, extra-lemniscal sensory modality only in patient 2. Both patients were treated with electrical PGS by means of a 4-pole electrode, the central sulcus being per-operatively located using the phase-reversal of the N20 wave of somatosensory evoked potentials. No sensory side effect, abnormal movement or epileptic seizure were observed during PGS. The analgesic effects were somatotopically distributed according to the localization of electrode on motor cortex. A satisfactory long-lasting pain control (60-70% on visual analog scale) as well as attenuation of nociceptive reflexes were obtained during PGS in the first patient. Pain relief was less marked and only transient (2 months) in patient 2, in spite of a similar operative procedure. In this patient, in whom PGS eventually evoked painful dysethesiae, no attenuation of nociceptive RIII reflex could be evidenced during PGS. Cerebral blood flow (CBF) was studied using emission tomography (PET) with O-labeled water. The sites of CBF increase during PGS were the same in both patients, namely the thalamus ipsilateral to PGS, cingulate gyrus, orbito-frontal cortex and brainstem. CBF increase in brainstem structures was greater and lasted longer in patient 1 while patient 2 showed a greater CBF increase in orbito-frontal and cingular regions. Our results suggest that PGS-induced analgesia is somatotopically mediated and does not require the integrity of somatosensory cortex and lemniscal system. PGS analgesic efficacy may be mainly related to increased synaptic activity in the thalamus and brainstem while changes in cingulate gyrus and orbito-frontal cortex may be rather related to attentional and/or emotional processes. The inhibitory control on pain would involve thalamic and/or brainstem relays on descending pathways down to the spinal cord segments, leading to a depression of nociceptive reflexes. Painful dysesthesiae during stimulation have to be distinguished from other innocuous sensory side effects, since they may compromise PGS efficacy.

To determine the usefulness of [18F]fluorodeoxyglucose (FDG) whole body FDG-PET in the diagnosis of tumours in patients with paraneoplastic neurological syndromes (PNS), we prospectively studied 20 patients with paraneoplastic antibodies in whom conventional imaging gave negative or inconclusive results for the presence of tumour. All 20 patients had neurological manifestations compatible with PNS and well-characterized paraneoplastic antibodies (12 anti-Hu, one anti-Hu and anti-CV2, one anti-CV2, four anti-Yo, one anti-Ri and one anti-amphiphysin). The mean delay between the onset of neurological symptoms and FDG-PET was 10 months (range 1-54). In these 20 patients, abnormal uptake was demonstrated in 18 patients, with some patients having abnormal signal in several areas. We observed abnormal uptake in the mediastinum (13 cases), lung (two cases), breast (two cases), parotid gland (one case), or the cervical, supraclavicular or axillary lymph nodes (seven cases). Following FDG-PET, the histological diagnosis of the tumour was made in 14 patients (small cell lung carcinoma in eight cases, breast adenocarcinoma in two, lung adenocarcinoma in two, axillary metastasis of ovary carcinoma in one, and malignant thymoma in one). Two other patients with abnormal FDG uptake showed radiological evidence of lung cancer, but a histological diagnosis could not be obtained. In two other patients, initial FDG-PET showed abnormal FDG uptake that was not confirmed a few months later by repeat FDG-PET. In the two patients with negative FDG-PET, peritoneal carcinomatosis was diagnosed in one and no tumour was found in the other. In our series, the sensitivity of FDG-PET for tumour detection was >83% demonstrating a clear role of this technique in the management of patients with PNS. However, in our series, the specificity of FDG uptake was only 25% due to unexplained abnormal FDG uptake in three patients and in abnormal FDG uptake due to a benign tumour in one patient. Over the study period, we saw 73 other patients with PNS and paraneoplastic antibodies. A tumour was demonstrated in 71 out of 73 by conventional techniques. Since false-positive and false-negative results are possible with FDG-PET and in most patients with PNS, the tumour is demonstrated by conventional techniques, we believe that FDG-PET should be reserved, at the moment, for patients with well-defined PNS antibodies when conventional imaging fails to identify a tumour or when lesions are difficult to biopsy.

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Brain areas activated in human male sexual behavior have not been characterized precisely. For the first time, positron emission tomography (PET) was used to identify the brain areas activated in healthy males experiencing visually evoked sexual arousal. Eight male subjects underwent six measurements of regional brain activity following the administration of [15O]H2O as they viewed three categories of film clips: sexually explicit clips, emotionally neutral control clips, and humorous control clips inducing positive but nonsexual emotions. Statistical Parametric Mapping was used to identify brain regions demonstrating an increased activity associated with the sexual response to the visual stimulus. Visually evoked sexual arousal was characterized by a threefold pattern of activation: the bilateral activation of the inferior temporal cortex, a visual association area; the activation of the right insula and right inferior frontal cortex, which are two paralimbic areas relating highly processed sensory information with motivational states; and the activation of the left anterior cingulate cortex, another paralimbic area known to control autonomic and neuroendocrine functions. Activation of some of these areas was positively correlated with plasma testosterone levels. Although this study should be considered preliminary, it identified brain regions whose activation was correlated with visually evoked sexual arousal in males.

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