Brain metabolism patterns are sensitive to attentional effort associated with a tone recognition task

Cortical and subcortical gray matter changes in patients with chronic tinnitus sustaining after vestibular schwannoma surgery

Tinnitus is attributed to partial sensory deafferentation resulting in a central maladaptive neuroplasticity. Unfortunately, the agent of deafferentation is usually unknown or irreversible. In patients with unilateral vestibular schwannoma (VS), however, the auditory nerve is affected by a benign tumor. Hence, removal of the tumor can cease the tinnitus. In turn, sustaining complaints after surgery indicate cortical neuroplasticity. The present study is a cross sectional study which aims to track cortical structural changes by surface-based morphometry in 46 VS patients with sustained (i.e. centralized) or ceased (i.e. peripheral) tinnitus after surgery. A volumetric analysis of cortical and subcortical gray matter (GM) anatomy was performed on preoperative high-resolution MRI and related to the presence of hearing impairment, pre- and/or postoperative tinnitus. Patients with sustained (i.e. chronic) tinnitus showed an increased GM volume of the bilateral caudate nucleus, the contralateral superior colliculus, the middle frontal and middle temporal gyrus, the fusiform gyrus as well as the ipsilateral pars orbitalis when compared to those patients in whom tinnitus ceased postoperatively. Chronic tinnitus in VS patients is associated with characteristic structural changes in frontal, temporal and subcortical areas. Notably, a significant GM change of the caudate nucleus was detected providing further support for the striatal gaiting model of tinnitus.

The biology of schizophrenia

Schizophrenia is an illness where the clinical signs and symptoms, course, and cognitive characteristics are well described. Successful pharmacological treatments do exist, even though they are likely palliative. However, this broad knowledge base has not yet led to the identification of its pathophysiology or etiology The risk factors for schizophrenia are most prominently genetic and scientists anticipate that contributions from the new genetic information in the human genome will help progress towards discovering a disease mechanism. Brain-imaging techniques have opened up the schizophrenic brain for direct inquiries, in terms of structure, neurochemisiry, and function. New proposals for diagnosis include grouping schizophrenia together with schizophrenia-related personality disorders into the same disease entity, and calling this schizophrenia spectrum disorder. New hypotheses of pathophysiology do not overlook dopamine as playing a major role, but do emphasize the participation of integrative neural systems in the expression of the illness and of the limbic system in generating symptoms. Critical observations for future discovery are likely to arise from molecular genetics, combined with hypothesis-generating experiments using brain imaging and human postmortem tissue.

Task difficulty in a simultaneous face matching task modulates activity in face fusiform area

The level of difficulty of a task can alter the neural network that activates for performance of the task. Previous studies have shown increased activation with task difficulty in the frontal lobes while the effects in the extrastriate visual areas have been unclear. We hypothesized that the face fusiform area (FFA), an area specialized for face processing, would increase activation as task difficulty increased in a face matching task. The difficulty level was increased by degrading the quality of the images. The degradation levels were 10%, 20%, 40% and 60%. Based on the correct response rate, the data were divided into a baseline level (composed of non-degraded and 10% degraded images) and a difficult level (composed of the 20%, 40% and 60% degraded images). Brain activation was measured using functional magnetic resonance imaging. The baseline face matching task activated a wide network of regions that included bilaterally the occipital, temporal and parietal lobes and the right frontal lobe. A novel behavioral finding was that task difficulty did not linearly increase with image degradation. The novel brain imaging finding was that the FFA is modulated by task difficulty and performance in the task was linearly correlated to activation in FFA. In addition, we found that activation in the dorsolateral prefrontal cortex (DLPFC) had increased activation as task difficulty increased. When adding the response time as a covariate, the differences in the DLPFC did not remain statistically significant. Increased task difficulty also led to a decrease in activation of visual areas in the extrastriate cortex. Task difficulty increased activation in the FFA to enhance the face processing and suppressed activation in visual extrastriate areas that processed low level properties of the stimuli. Task difficulty led to enhanced response in the FFA and suppressed response in other visual areas.

Probing the human hippocampus using rCBF: contrasts in schizophrenia

Regional cerebral blood flow (rCBF) data from two PET-15O water schizophrenia studies were analyzed using individually placed, magnetic resonance (MR)-guided hippocampal volumes of interest (VOI). In one study, normal (N = 10) and schizophrenic (N = 18) volunteers performed an overlearned auditory discrimination task in rest, control, and decision conditions. In the other study, schizophrenic and normal volunteers received the noncompetitive NMDA receptor antagonist ketamine and placebo and had sequential rCBF evaluations. Moreover, the schizophrenic volunteers were off drug in one study and on antipsychotic drug in the second study, allowing an additional comparison of medication status. VOIs were placed on anterior, middle, and posterior hippocampal areas in each PET image from both studies, redirected from an MR scan, and individually adjusted. While no hippocampal activation was apparent in either the normal or schizophrenic group in the task vs. condition comparison, rCBF was higher in the schizophrenic than in the normal hippocampus in both task and control conditions, independently. In addition, at rest rCBF was significantly higher in the unmedicated group of schizophrenics than in the group of medicated patient volunteers and higher than in the normal comparison group. This suggests that schizophrenia is associated with elevated rCBF in the hippocampus, which "normalizes" with antipsychotic drug treatment. Ketamine, the noncompetitive NMDA receptor antagonist, was more potent in reducing rCBF in the schizophrenic group compared to the normal volunteer group. These data are consistent with a previous report from our laboratory of reduced NMDA receptor NR1 subunit expression and possible abnormal NMDA receptor composition in schizophrenia. These data show an abnormality of hippocampal function in schizophrenia and suggest that this abnormality may be associated with the pathophysiology of the illness.