Auditory Cortex In Patients Research Articles

RTMS for the treatment of auditory phantom perceptions

The pathophysiological mechanisms of idiopathic tinnitus remain unclear. Recent studies demonstrated focal brain activation in the auditory cortex of patients suffering from chronic tinnitus. Low frequency repetitive transcranial magnetic stimulation (rTMS) is able to reduce cortical hyperexcitability. Patients suffering from severe chronic tinnitus underwent a [18F]deoxyglucose- PET (positron emission tomography) and MRI (magnetic resonance imaging) measurement. Fusioning of the individual PET scan with the structural MRI-scan (T1, MPRAGE) allowed to exactly identify the area of increased metabolic activity in the auditory cortex, which was selected as the target point for rTMS. In this context, a neuronavigational system adapted for TMS positioning enabled to monitore the exact position of the figure 8-shaped magnetic coil in relation to the target area. rTMS (110% motor threshold; 1 Hz; 2000 stimuli/ day over 10 days) was performed using a placebo controlled design. Patients were blind regarding the stimulus condition. For the sham stimulation a specific sham-coil system was used. Treatment outcome was assessed with a specific tinnitus questionnaire (Goebel and Hiller). Up to date, 30 patients were included. In most of the patients we could localize an increased metabolic activation within the primary auditory cortex. After 10 days of verum rTMS a remarkable improvement of the tinnitus score was found. This effect could not be seen after sham stimulation.

Long-term effects of repetitive transcranial magnetic stimulation (rTMS) in patients with chronic tinnitus

The pathophysiologic mechanisms of idiopathic tinnitus remain unclear. Recent studies demonstrated focal brain activation in the auditory cortex of patients with chronic tinnitus. Low-frequency repetitive transcranial magnetic stimulation (rTMS) is able to reduce cortical hyperexcitability. Fusing of the individual PET-scan with the structural MRI-scan (T1, MPRAGE) allowed us to identify exactly the area of increased metabolic activity in the auditory cortex of patients with chronic tinnitus. With the use of a neuronavigational system, this target area was exactly stimulated by the figure 8-shaped magnetic coil. In a prospective study, rTMS (110% motor threshold; 1 Hz; 2000 stimuli/day over 5 days) was performed using a placebo controlled cross-over design. Patients were blinded regarding the stimulus condition. For the sham stimulation a specific sham-coil system was used. Fourteen patients were followed for 6 months. Treatment outcome was assessed with a specific tinnitus questionnaire (Goebel and Hiller). Tertiary referral medical center. Increased metabolic activation in the auditory cortex was verified in all patients. After 5 days of verum rTMS, a highly significant improvement of the tinnitus score was found whereas the sham treatment did not show any significant changes. The treatment outcome after 6 months still demonstrated significant reduction of tinnitus score. These preliminary results demonstrate that neuronavigated rTMS offers new possibilities in the understanding and treatment of chronic tinnitus.

Aberrant localization of synchronous hemodynamic activity in auditory cortex reliably characterizes schizophrenia

BackgroundAmong the most prominent features of schizophrenic brains are abnormalities in auditory cortex structure and function, particularly in the superior temporal gyrus (STG). In this study, we attempted to examine auditory cortex function using an intrinsic, task-uncorrelated measure. MethodsUsing functional magnetic resonance imaging data, we calculated synchronous hemodynamic independent maps (SHIMs) of auditory cortex in patients with schizophrenia and matched healthy control subjects while they performed an auditory oddball task. ResultsPatient SHIMs revealed greater synchrony in ventral and medial STG regions (including auditory association Brodmann area [BA] 42); control SHIMs had greater synchrony in dorsal and lateral STG regions (which did not include BA 42). A within-participant subtractive comparison of these two sets of regions differentiated schizophrenic from healthy control subjects with 97% accuracy initially (further validated by a retest of the healthy control subjects) and performed with 94% accuracy in a confirmatory study of new subjects scanned at a different site. ConclusionsThese results shed new light on STG functional differences in schizophrenia, suggest that aberrant patterns of coherence in temporal lobe cortical regions are a cardinal abnormality in schizophrenia, and have the potential to provide a powerful, quantitative clinical tool for the assessment of schizophrenia.

Enhanced activation of the auditory cortex in patients with inner-ear hearing impairment: a magnetoencephalographic study

Injury of peripheral auditory organ often induces abnormality of loudness sensation such as loudness recruitment. However, objective evaluation of this phenomenon has rarely been performed. To elucidate this abnormal loudness sensation, cortical mechanisms were investigated by recording auditory evoked magnetic fields (AEFs). We recorded AEFs in 8 patients suffering from inner-ear hearing impairment with loudness recruitment and in 14 healthy hearing controls using a 122-channel whole-head neuromagnetometer. Tone bursts of 1 kHz were presented monaurally at 4 different intensities (40, 50, 60, 70 dB HL) with a constant interstimulus interval of 1 s. In both groups, the 100 ms response (N100m) increased in amplitude and decreased in latency as a function of stimulus intensity in both hemispheres. Concerning the source strength, increment of dipole moment of N100m was more rapid according to the stimulus intensity in patients compared with that in healthy subjects. Source strength of N100m was enhanced at high stimulus intensity in patients, and its ratio to healthy subjects was 1.08 at 50 dB, 1.69 at 60 dB and 2.04 at 70 dB. In patients with inner-ear hearing impairment, enhanced activation of the auditory cortex was observed, and may help explain loudness recruitment.

FMRI of the auditory cortex in patients with unilateral carotid artery steno-occlusive disease.

To examine whether an internal carotid artery (ICA) steno-occlusive disease leads to a reduced blood oxygenation level dependent (BOLD)-signal change due to a decreased vasodilatory reserve capacity. Patients suffering from unilateral ICA stenosis or occlusion were examined using functional magnetic resonance imaging (fMRI) of the auditory cortex with a bilateral stimulation applying a pulsed 1000 Hz sine-tone. Compared to control subjects, who showed symmetric bilateral BOLD-responses within the auditory cortex, the ICA patients revealed either a normal bilateral cortical activation pattern or a reduced cortical activation on the steno-occluded side. This latter decrease of BOLD-signal change might indicate a depressed vasomotor reserve capacity. The observed coincidence between this asymmetric reduction in BOLD-signal and ischemic borderzone lesions on the affected side in this subgroup of patients strongly supports this assumption. This study shows that fMRI of the auditory cortex appears to have clinical merit in the workup of cerebrovascular conditions.

Transcranial Magnetic Stimulation of Left Auditory Cortex in Patients With Schizophrenia: Effects on Hallucinations and Neurocognition

The effects of transcranial magnetic stimulation (TMS) on hallucination severity and neurocognition were studied in 9 medication-resistant hallucinating patients. A statistically significant improvement was observed on a hallucination scale after 10 days of TMS at the left auditory cortex.

Cortical reorganization in patients with high frequency cochlear hearing loss

Animal research has shown that tonotopic representation in the auditory cortex is not statically fixed in the adult organism but can be altered after deafferentation. The present study examines the plasticity of the human auditory cortex in patients with high frequency cochlear hearing loss by means of magnetoencephalographic measurements. The data show that the cortical map can reorganize such that cortical neurons deprived of their usual most sensitive afferent input now respond to tone frequencies adjacent to the frequency range of the partial hearing loss. The results suggest that deafferentation due to cochlear damage in adults may lead to functional reorganization of auditory cortical structures.

502. Reduced neuropil in the auditory cortex of patients with schizophrenia

It has been hypothesized that there is a reduction in the interneuronal space in the prefrontal cortex in Schizophrenia (Selemon et al., 1995). Because the spatial distribution of neurons in the cortex is focused around the minicolumn, we anticipated that the hypothesis of reduced interneuronal space in schizophrenia could be independently tested by analysis of these units. Initial studies have focused on prefrontal cortex, areas 9 and 46. We investigated a small population of normal controls (n = 13) and schizophrenia patients (n = 7), diagnosed according to DSM III—R criteria. Patients and controls were age and sex matched. Photomicrographs of the posterior portion of the superior temporal gyrus (area Tpt) were taken at 100× magnification. Among the features examined was the amount of neuropil space in the periphery of cell columns where local circuits, synapses, and dendritic branches predominate. We also measured the amount of spacing between cell soma within the cell-dominant portion of the columns, and the distance separating cell columns in the horizontal plane. All the values for spacing distances and neuropil space were less in schizophrenic brains. Significant findings resulted when we combined the data for the right and left sides of both schizophrenics and controls. We conclude that neuropil space is decreased in Tpt in schizophrenia patients, with the greatest reduction occurring within the core of the cell column. The finding infers a generalized distribution of interneuronal space reduction in the schizophrenic brain.

Recording of auditory evoked potentials in man using chronic subdural electrodes.

With the aid of chronic subdural electrodes we have been able to record from the posterior banks of the sylvian fissure, auditory evoked potentials (AEPs) that had morphologies and peak latencies compatible with the primary AEPs described by Celesia and Puletti (1969). These AEPs had amplitudes that were not only affected by the side of stimulus presentation but were maximal in an area close to the primary auditory cortex. The AEPs also displayed an extremely steep spatial gradient and were not altered by pentobarbitone sodium and nitrous oxide anaesthesia. Together, these properties suggest that these subdurally recorded potentials are near-field evoked potentials from the primary auditory cortex. The focal nature of these potentials also allows them to be used as effective electrophysiological tools for localization of the primary auditory cortex in patients.