Gray matter-white matter contrast on spin-echo T1-weighted images at 3 T and 1.5 T: a quantitative comparison study

Discrepancies exist in the literature regarding contrast between gray and white matter on spin-echo (SE) T1-weighted MR imaging at 3 T. The present study quantitatively assessed differences in gray matter-white matter contrast on both single- and multi-slice SE T1-weighted imaging between 3 and 1.5 T. SE T1-weighted sequences with the same parameters at both 3 and 1.5 T were used. Contrast-to-noise ratio (CNR) between gray and white matter (CNR(GM-WM)) was evaluated for both frontal lobes. To assess the effects of interslice gap, multi-slice images were obtained with both 0 and 25% interslice gap. Single-slice CNR(GM-WM) was higher at 3 T (17.66 +/- 2.68) than at 1.5 T (13.09 +/- 2.35; P < 0.001). No significant difference in CNR(GM-WM) of multi-slice images with 0% gap was noted between 3 and 1.5 T (3T, 8.61 +/- 2.55; 1.5T, 7.43 +/- 1.20; P > 0.05). Multi-slice CNR(GM-WM) with 25% gap was higher at 3T (12.47 +/- 3.31) than at 1.5 T (9.73 +/- 1.37; P < 0.001). CNR(GM-WM) reduction rate of multi-slice images with 0% gap compared with single-slice images was higher at 3T (0.47 +/- 0.13) than at 1.5 T (0.38 +/- 0.09; P = 0.02). CNR(GM-WM) on single-slice SE T1-weighted imaging and CNR(GM-WM) on multi-slice images with 25% interslice gap were better at 3 T than at 1.5 T. The influence of multi-slice imaging on CNR(GM-WM) was significantly larger at 3T than at 1.5 T.

Heterospecific and conspecific social cognition in the anterior cingulate cortex

The development of human social cognition has allowed interactions with other species and the formation of a cooperative multi-species society. This feature posited keen attention on the following question: is heterospecific social cognition represented in the same brain areas as conspecific social cognition? Here we investigated brain activity accompanying the facial recognition of familiar humans and of companion dogs, both of whom had real social interactions with participants. The rostroventral anterior cingulate cortex responded to both species whereas the caudal anterior cingulate cortex was sensitive only to familiar humans. Social cognition processes may be dual-layered: the rostroventral anterior cingulate cortex is associated with fundamental and intuitive aspects, whereas the caudal anterior cingulate cortex is concerned with the analysis of complex social interactions.

Gliomatosis Cerebri Presenting as a Parkinsonian Syndrome

We report a 70-year-old man who was hospitalized after a left-sided partial seizure progressed to grand mal seizures. Three years before, the patient had presented with the main symptoms of bradykinesia and gait disturbance and was diagnosed with parkinsonism resistant to L-dopa. At the latest admission, extensive diffuse white matter high-intensity areas were present on T2-weighted magnetic resonance imaging images, and stereotactic brain biopsy showed that these lesions were gliomatosis cerebri (GC). This is the first reported case in which extensive lesions in the bilateral white matter have been associated with parkinsonism as the main clinical feature; only one other case has been reported in which GC presented as parkinsonism, and this differed from the current case with respect to localization and symptoms. We speculate that damage to the thalamocortical projections and functional impairment due to demyelination could have caused parkinsonism in our patient, and we discuss the differential diagnosis.

Neural correlates of regional EEG power change

To clarify the physiological significance of task-related change of the regional electroencephalogram (EEG) rhythm, we quantitatively evaluated the correlation between regional cerebral blood flow (rCBF) and EEG power. Eight subjects underwent H2 15O positron emission tomography scans simultaneously with EEG recording during the following tasks: rest condition with eyes closed and open, self-paced movements of the right and left thumb and right ankle. EEG signals were recorded from the occipital and bilateral sensorimotor areas. Cortical activation associated with EEG rhythm generation was studied by the correlation between rCBF and EEG power. There were significant negative correlations between the sensorimotor EEG rhythm at 10-20 Hz on each side and the ipsilateral sensorimotor rCBF and between the occipital EEG rhythm at 10-20 Hz and the occipital rCBF. The occipital EEG rhythm showed a positive correlation with the bilateral medial prefrontal rCBF, while the right sensorimotor EEG rhythm showed a positive correlation with the left prefrontal rCBF. In conclusion, decrease in the regional EEG rhythm at 10-20 Hz might represent the neuronal activation of the cortex underlying the electrodes, at least for the visual and sensorimotor areas. The neural network including the prefrontal cortex could play an important role to generate the EEG rhythm.

Stimulus-related 20-Hz activity of human cortex modulated by the way of presenting hand actions

The neural mechanisms underlying recognition of presented hand actions are not well understood. Rolandic rhythmic activity of about 20 Hz is reproducibly induced after median nerve stimulation and has been reported to be related to various types of movements including actual movement, motor imagery and action observation. We recorded neuromagnetic brain activity from 11 healthy subjects to investigate whether the way to present hand actions modulates the 20-Hz activity after median nerve stimulation. The stimulus-related 20-Hz activity was prominently evoked in the contralateral sensorimotor cortex around 0.5-1.0 s after median nerve stimulation and was almost completely suppressed during executing actual hand action. The suppression of the stimulus-related 20-Hz activity was also observed during viewing the similar action of another person's hand. Furthermore, the suppression during viewing the action of another person's hand presented in the same direction as the subject's hand was significantly larger than that during viewing it presented in the opposite direction and was closer to that during executing subject's own hand action. These results indicate that the stimulus-related rolandic 20-Hz activity was modulated by the way to present hand actions, and suggest that the 20-Hz activity is related to neural mechanisms underlying recognition of presented hand actions.

Clinical significance of preoperative fibre-tracking to preserve the affected pyramidal tracts during resection of brain tumours in patients with preoperative motor weakness

OBJECTIVE

To clarify the clinical usefulness of preoperative fibre-tracking in affected pyramidal tracts for intraoperative monitoring during the removal of brain tumours from patients with motor weakness.

METHODS

We operated on 10 patients with mild to moderate motor weakness caused by brain tumours located near the pyramidal tracts under local anaesthesia. Before surgery, we performed fibre-tracking imaging of the pyramidal tracts and then transferred this information to the neuronavigation system. During removal of the tumour, motor function was evaluated with motor evoked potentials elicited by cortical/subcortical electrical stimulation and with voluntary movement.

RESULTS

In eight patients, the locations of the pyramidal tracts were estimated preoperatively by fibre-tracking; motor evoked potentials were elicited on the motor cortex and subcortex close to the predicted pyramidal tracts. In the remaining two patients, in which fibre-tracking of the pyramidal tracts revealed their disruption surrounding the tumour, cortical/subcortical electrical stimulation did not elicit responses clinically sufficient to monitor motor function. In all cases, voluntary movement with mild to moderate motor weakness was extensively evaluated during surgery and was successfully preserved postoperatively with appropriate tumour resection.

CONCLUSIONS

Preoperative fibre-tracking could predict the clinical usefulness of intraoperative electrical stimulation of the motor cortex and subcortical fibres (ie, pyramidal tracts) to preserve affected motor function during removal of brain tumours. In patients for whom fibre-tracking failed preoperatively, awake surgery is more appropriate to evaluate and preserve moderately impaired muscle strength.

Concurrence of non-myasthenic symptoms with myasthenia gravis

Myasthenia gravis (MG) is a disease that is known to be accompanied by various complications. But the relationship between these complications and MG and the treatment for these complications still partly remain unknown. We report two cases of MG with unusual complications. The first one is a case of a 72-year-old woman with lingual dyskinesia, and the second is a 28-year-old man with dysgeusia. Both symptoms improved in parallel after the treatment of MG. Here we report these cases and review similar cases in the literature.

Diffusion tensor fiber tractography for arteriovenous malformations: quantitative analyses to evaluate the corticospinal tract and optic radiation

BACKGROUND AND PURPOSE

We hypothesized that diffusion tensor fiber tractography would be affected by intracranial arteriovenous malformation (AVM). The purpose of the present study was to evaluate the influence of intracranial AVM on corticospinal tract and optic radiation tractography.

MATERIALS AND METHODS

The subject group comprised 34 patients with untreated intracranial AVM. Hemorrhage was present in 13 patients and absent in 21 patients. Perinidal fractional anisotropy (FA) and number of voxels along the reconstructed corticospinal and optic radiation tracts were measured, and left-to-right asymmetry indices (AIs) for those values were quantified. Patients were assigned to 1 of 3 groups: tracts distant from nidus, tracts close to nidus without neurologic symptoms, and tracts close to nidus associated with neurologic symptoms. One-way analysis of variance was used to compare differences in AI between groups. Hemorrhagic and nonhemorrhagic groups were assessed separately.

RESULTS

In patients without hemorrhage, AI of optic radiation volume (P<.0001), AI of perinidal FA along corticospinal tract (P=.006), and optic radiation (P=.01) differed significantly between groups. In patients associated with hemorrhage, AI of corticospinal tract volume (P=.01), AI of perinidal FA along corticospinal tract (P=.04), and optic radiation (P=.004) differed significantly between groups.

CONCLUSIONS

Corticospinal tract and optic radiation tractography were visualized in patients with AVM. In patients with both hemorrhagic and nonhemorrhagic AVM, the 2 fiber tracts close to the nidus were less visualized in the affected hemisphere than those distant from the nidus. Tracts were less visualized in patients with neurologic symptoms than in asymptomatic patients.

The lack of expression of the peripheral benzodiazepine receptor characterises microglial response in anaplastic astrocytomas

The peripheral benzodiazepine receptor (PBR) is a 18 kDa molecule mainly involved in cholesterol transport through the mitochondrial membrane. In microglia, PBR is expressed from the earliest stages of activation and appears to exert a pro-inflammatory function. This molecule is commonly up-regulated in inflammatory, degenerative, infective and ischaemic lesions of the central nervous system but it has never been reported in glioma-infiltrating microglia. We examined two anaplastic astrocytomas showing minimal contrast-enhancement and therefore little damage of the blood brain barrier to minimise the presence of blood borne macrophages within tumour tissue. The two lesions were studied in vivo using positron emission tomography (PET) with the specific PBR ligand [(11)C](R)-PK11195 and the corresponding tumour tissue was investigated with an anti-PBR antibody. Glioma-infiltrating microglia were characterised for molecules involved in antigen presentation and cytotoxic activity. As comparison, PBR was investigated in three brains with multiple sclerosis (MS) and three with Parkinson's disease (PD). The expression profile of four anaplastic astrocytomas was also exploited and results were compared to the profile of eleven samples of normal temporal lobe and nine cases of PD. PET studies showed that [(11)C](R)-PK11195 binding was markedly lower in tumours than in the contralateral grey matter. Pathological investigation revealed that glioma-infiltrating microglia failed to express PBR and cytotoxic molecules although some cells still expressed antigen presenting molecules. PBR and cytotoxic molecules were highly represented in MS and PD. Evaluation of microarray datasets confirmed these differences. Our results demonstrated PBR suppression in glioma-infiltrating microglia and suggested that PBR may have a relevant role in modulating the anti-tumour inflammatory response in astrocytic tumours.

Somatotopy of corticospinal tract in the internal capsule shown by functional MRI and diffusion tensor images

Using functional MRI and diffusion tensor tractography, we studied the topographical relation of hand and foot fibers of the corticospinal tract within the internal capsule to verify the recent unexpected finding by Holodny et al., who reported that hand fibers are located anterolateral to foot fibers, not anteromedial as is currently believed. The location of hand fibers with respect to foot fibers was anterolateral in four participants, posterolateral in two, and anteromedial in one of seven participants examined. Thus, there was some support for the anterolateral finding of Holodny et al., but interindividual variability was also indicated.

Clinical impact of integrated functional neuronavigation and subcortical electrical stimulation to preserve motor function during resection of brain tumors

OBJECT

The authors evaluated the clinical impact of combining functional neuronavigation with subcortical electrical stimulation to preserve motor function following the removal of brain tumors.

METHODS

Forty patients underwent surgery for treatment of brain tumors located near pyramidal tracts that had been identified by fiber tracking. The distances between the electrically stimulated white matter and the pyramidal tracts were measured intraoperatively with tractography-integrated functional neuronavigation, and correlated with subcortical motor evoked potentials (MEPs) and clinical symptoms during and after resection of the tumors. Motor function was preserved after appropriate tumor resection in all cases. In 18 of 20 patients, MEPs were elicited from the subcortex within 1 cm of the pyramidal tracts as measured using intraoperative neuronavigation. During resection, improvement of motor weakness was observed in two patients, whereas transient mild motor weakness occurred in two other patients. In 20 patients, the distances between the stimulated subcortex and the estimated pyramidal tracts were more than I cm, and MEPs were detected in only three of these patients following stimulation.

CONCLUSIONS

Intraoperative functional neuronavigation and subcortical electrical stimulation are complementary techniques that may facilitate the preservation of pyramidal tracts around 1 cm of resected tumors.

Transcranial magnetic stimulation (TMS) applied to left dorsolateral prefrontal cortex disrupts verbal working memory performance in humans

Working memory refers to the temporary maintenance and processing of information and involves executive processes that manipulate the contents of the working memory. The role of the executive function in the human left dorsolateral prefrontal cortex (LDLPFC) was explored using transcranial magnetic stimulation (TMS) after confirming the LDLPFC activation using fMRI. We applied double-pulse TMS having a 100-ms inter-pulse interval to LDLPFC immediately after the subjects finished reading the sentences of the reading span test (RST) task, an efficient measure of verbal working memory, in which dual tasks that include both sentence comprehension and word maintenance are required. Using eight normal participants, we found a significant deterioration of performance, i.e., decreased number of correctly reported words, in RST due to TMS stimulation of LDLPFC. Evidence suggests that transient functional disruption of the LDLPFC impairs performance in the maintenance processing of the RST task.

Directional disorientation following left retrosplenial hemorrhage: a case report with fMRI studies

We report a 55-year-old right-handed man who presented with topographical disorientation following left retrosplenial hemorrhage. His directional information about familiar places, encoded by previous navigation, was severely impaired, and he could not learn the direction to new places in large-scale spaces beyond the range of visual surveillance. By contrast, he had no difficulties with directional information encoded in a tabletop manner: he could locate major cities or countries on a map, and he also could memorize the spatial relationship of objects in a room. Six months after the ictus, when he had recovered from his directional disorientation, a functional magnetic resonance imaging (fMRI) study of mental navigation demonstrated prominent activation in the retrosplenial area along the right parieto-occipital sulcus and the circumference of the injured area on the left side. The present study, together with previous investigations including clinical case reports, functional neuroimaging, and anatomical and physiological studies on monkeys, suggests that the 'sense of direction' in a large-scale locomotor environment is subserved by the visual area along the parieto-occipital sulcus, and that bilateral deterioration of this function causes directional disorientation.

Anterior cingulate pathology and social cognition in schizophrenia: a study of gray matter, white matter and sulcal morphometry

The anterior cingulate gyrus (ACG) is a critical structure for social cognitive processing; the pathology of this structure might be a major source of social dysfunction in schizophrenia. Multiple structural abnormalities of the ACG have been demonstrated in schizophrenia including changes in gray matter volume, white matter microstructures and macroscopic sulcal morphology. However, the interrelationships among these different abnormalities have not been investigated. Thus, the relationship between structural abnormalities in the ACG and social cognition in schizophrenia remains to be elucidated. Magnetic resonance imaging data were acquired at 3.0 T from 26 schizophrenic patients and 20 healthy participants. We performed anterior cingulate cortex (ACC) volumetry, evaluated diffusion tensor imaging of the anterior cingulum, analyzed paracingulate/cingulate sulcus (PCS/CS) morphology and investigated the interrelationships among these measures. We also investigated the association between ACG structural abnormalities and psychopathology, and the social cognition ability of schizophrenic patients as estimated by emotion attribution tasks. Compared with healthy subjects, schizophrenic patients exhibited reduced ACC volume, decreased fractional anisotropy in the anterior cingulum bilaterally and a poorly developed PCS/CS in the left hemisphere. No interrelationship was identified among these measures in the schizophrenic group. Schizophrenic patients performed poorly on emotion attribution tasks. Importantly, clinical symptoms and performance on emotion attribution subtasks were associated with ACC volumes and left PCS/CS variation in different ways. These results suggested that pathology of the ACC, anterior cingulum and PCS/CS is, at least partially, independent and has differential impacts on psychopathology and social cognitive impairment in schizophrenia.

Functional coupling of human prefrontal and premotor areas during cognitive manipulation

Evidence indicates the involvement of the rostral part of the dorsal premotor cortex (pre-PMd) in executive processes during working memory tasks. However, it remains unclear what the executive function of pre-PMd is in relation to that of the dorsolateral prefrontal cortex (DLPFC) and how these two areas interact. Using functional magnetic resonance imaging (fMRI), brain activity was examined during a delayed-encoding recognition task. Fifteen subjects had prelearned several four-code standard sequences and super sequences (SUPs) consisting of a train of two standard sequences to form "chunks" in long-term memory. During fMRI, subjects remembered eight-code encoding stimuli presented as an SUP or two unlinked standard sequences (2STs). A memory probe prompted the subjects to recognize codes across two chunks (ACROSS) or within a single chunk. A 2 x 2 factorial design was used to test two types of working memory manipulation: (1) a reductive operation selecting codes from chunks ("segmenting") and (2) a synthetic operation converting unlinked codes into a sequence ("binding"). Response time data supported the behavioral effects of each operation. Event-related fMRI showed that the "segmenting operation" activated the DLPFC bilaterally, whereas the "binding operation" enhanced the left pre-PMd activity. Activity in the ventrolateral prefrontal cortex suggested its involvement in the retrieval of task-relevant information from long-term memory. Furthermore, effective connectivity analysis indicated that the left pre-PMd and ipsilateral DLPFC interacted specifically during the ACROSS recognition of 2STs, the condition that involved both operations. We propose specific neural substrates for working memory manipulation: the DLPFC for segmenting/attentional selection and the pre-PMd for binding/sequencing. The functional coupling between the DLPFC and pre-PMd appears to play a role in combining these distinct operations.

Cognitive slowing in Parkinson disease is accompanied by hypofunctioning of the striatum

Objective: To investigate whether cognitive slowing in Parkinson disease (PD) reflects disruption of the basal ganglia or dysfunction of the frontal lobe by excluding an influence of abnormal brain activity due to motor deficits.

Methods: We measured neuronal activity during a verbal mental-operation task with H215O PET. This task enabled us to evaluate brain activity change associated with an increase in the cognitive speed without an influence on motor deficits.

Results: As the speed of the verbal mental-operation task increased, healthy controls exhibited proportional increase in activities in the anterior striatum and medial premotor cortex, suggesting the involvement of the corticobasal ganglia circuit in normal performance of the task. By contrast, patients with PD lacked an increase in the striatal activity, whereas the medial premotor cortex showed a proportional increase.

Conclusions: Although the present study chose a liberal threshold and needs subsequent confirmation, the findings suggest that striatal disruption resulting in abnormal processing in the corticobasal ganglia circuit may contribute to cognitive slowing in Parkinson disease, as is the case in motor slowing.

Quantification of nicotinic acetylcholine receptors in Parkinson's disease with (123)I-5IA SPECT

We quantified in vivo brain nicotinic acetylcholine receptor (nAChR) distributions in patients with Parkinson's disease (PD) and evaluated correlations between nAChR distributions and clinical variables of the patients, especially dopaminergic medications. Ten patients with PD without dementia underwent 5-(123)I-iodo-3-(2(S)-azetidinylmethoxy)pyridine ((123)I-5IA) single photon emission computed tomography (SPECT) and the data were compared with those of 10 age-matched healthy volunteers. Correlation analyses between (123)I-5IA distribution volumes (DVs) in each brain region and clinical variables of the patients were also performed. The PD group showed a statistically significant decrease (20-25%) in the brainstem and frontal cortex as compared with the control group. Although age, duration of disease, daily dose of levodopa, duration of PD medication use, and scores on the motor section of Unified Parkinson's Disease Rating Scale were not significantly correlated with DV values in any brain regions, high daily doses of dopamine agonist showed a significant negative correlation with DVs in the cerebellum, and temporal, parietal and occipital cortices. These findings suggest that patients with PD without dementia can show reductions especially in the brainstem and frontal cortex. They also suggest that dopamine agonists can have a negative influence on the distribution of nAChRs.

Subregions of human parietal cortex selectively encoding object orientation

Computation of object orientation could be an independent process from those of other object features, but currently neither the location of human brain areas selectively coding orientation information nor an optimum experimental paradigm have yet been established. In this study, functional magnetic resonance imaging was used to investigate brain activation in the parietal cortices related to object orientation. Using an Arabic digit whose spatial attributes were carefully manipulated, we found parietal areas exclusively sensitive to object orientation, but not to general spatial attention. It seems that, by excluding confounds such as mental manipulation or working memory as well as inherent spatial information within the stimuli, functional segregation within the parietal lobe can be effectively probed.

The role of left and right intraparietal sulcus in the attentional blink: a transcranial magnetic stimulation study

Processing of one visual target (T1) makes it difficult to become aware of a second target (T2), when two targets, embedded in a stream of distractor stimuli, occur within about 500 ms. This phenomenon is known as attentional blink (AB) and reflects the temporal limitation in allocating visual attention. Although several studies suggest that parietal regions are concerned with the AB phenomenon, their functional relevance remains unclear. We investigated whether left and/or right intraparietal sulcus (IPS) contributed to the AB bottleneck using transcranial magnetic stimulation (TMS). The course of recovery from the AB deficit was facilitated when single pulse TMS induced a transient interruption of left or right IPS activity at a T1-TMS stimulus onset asynchrony of 350 ms, while there was no effect of TMS or sham stimulation delivered over Cz with the same timing. These results provide direct evidence that activation of left as well as right IPS is involved in the genesis of AB. This finding supports the idea that the IPS plays a critical role in the cortical network controlling the temporal dynamics of visual awareness.

Placebo analgesia: a PET study

Placebo analgesia involves complex mechanisms and sometimes has a marked effect on patients in pain. In this study we examined changes in regional cerebral blood flow (rCBF) under three different conditions (resting, hot, painful) before and after placebo administration using H(2)(15)O and positron emission tomography in ten healthy subjects. In five subjects, placebo administration significantly decreased pain-intensity score (placebo responders), and rCBF in the medial prefrontal cortex (MPFC), posterior parietal cortex (PPC), and inferior parietal lobe (IPL) increased after placebo administration compared with before placebo administration under the painful condition. Furthermore, in the placebo responders, rCBF in the MPFC, PPC and IPL also increased under the resting condition (without sensory stimulation) after placebo administration compared with before placebo administration. However, there was no rCBF change under the rest condition in the placebo nonresponders after placebo administration. These results suggest that placebo analgesia has its effect under the resting condition and MPFC, IPL and PPC may have an important role in placebo analgesia.

Comparison between motor evoked potential recording and fiber tracking for estimating pyramidal tracts near brain tumors

OBJECT

The utility of subcortical electrical stimulation and fiber tracking were compared to estimate the pyramidal tract near brain tumors.

METHODS

In 22 patients, the white matter at the bottom of a tumor was electrically stimulated near the fiber tracking of the pyramidal tract shown on a neuronavigation system. The distance between the center of the fiber tracking of these tracts and the stimulated region was measured and defined as the motor evoked potential (MEP) response. The MEP was consistently produced at distances less than 7 mm (six patients), but was consistently absent at distances more than 13 mm (seven patients) from the fiber tracking of the pyramidal tracts. In the nine patients in whom the distance was between 8 and 12 mm, an MEP was elicited when stimulation was applied at the level of the corona radiata. Motor function was preserved or even improved with appropriate tumor resection in all patients.

CONCLUSIONS

The anteroposteriorly running superior longitudinal fasciculus could cause complications in the fiber tracking of upper-extremity motor pathways at the level of the corona radiata. During resection of tumors located near the corona radiata, subcortical electrical stimulation should be applied at some distance from the pyramidal tract, as estimated by fiber tracking.

[Clinical applications of molecular imaging methods for patients with ischemic stroke]

Several molecular imaging methods have been developed to visualize pathophysiology of cerebral ischemia in humans in vivo. PET and SPECT with specific ligands have been mainly used as diagnostic tools for the clinical usage of molecular imaging in patients with ischemic stroke. Recently, cellular MR imaging with specific contrast agents has been developed to visualize targeted cells in human stroke patients. This article reviews the current status in the clinical applications of those molecular imaging methods for patients with ischemic stroke.

A recovery from enhancement of activation in auditory cortex of patients with idiopathic sudden sensorineural hearing loss

OBJECTIVE

We previously reported enhanced activation of auditory cortex in patients with bilateral chronic inner-ear hearing loss. To determine whether this enhancement can exhibit a short-term alteration, we measured auditory evoked magnetic fields (AEFs) in patients with idiopathic sudden sensorineural hearing loss (ISSHL) in the acute phase (AP) and recovery phases (RPs).

METHODS

We recorded AEFs in two unilateral ISSHL patients at three time points (AP, RP1, and RP2) using a whole-head neuromagnetometer. Tone bursts of 1 kHz were presented monaurally to the affected and healthy ear at four different intensities (40-70 dB HL).

RESULTS

Both patients showed the enhancement of N100 m moment at AP and not at RPs in response to the affected ear stimulation, and stronger N100 m moment in ipsilateral than contralateral hemisphere in response to the healthy ear stimulation at AP.

CONCLUSIONS

Enhancement of N100 m amplitude occurs in ISSHL patients and disappears on the scale of days. Enhancement of activity in the auditory cortex derived from inner-ear hearing loss can thus exhibit short-term change.

SIGNIFICANCE

The results of this study provide first evidence for a recovery from enhancement of activation in the auditory cortex following injury of peripheral hearing organ.