Elsa van der Loo

The neural correlates of tinnitus-related distress

Tinnitus is an auditory phantom percept with a tone, hissing, or buzzing sound in the absence of any objective physical sound source. About 6% to 25% of the affected people report interference with their lives as tinnitus causes a considerable amount of distress. However, the underlying neurophysiological mechanism for the development of tinnitus-related distress remains not well understood. Hence we focus on the cortical and subcortical source differences in resting-state EEG between tinnitus patients with different grades of distress using continuous scalp EEG recordings and Low Resolution Electromagnetic Tomography (LORETA). Results show more synchronized alpha activity in the tinnitus patients with a serious amount of distress with peaks localized to various emotion-related areas. These areas include subcallosal anterior cingulate cortex, the insula, parahippocampal area and amygdala. In addition, less alpha synchronized activity was found in the posterior cingulate cortex, precuneus and DLPFC. A comparison between the tinnitus group with distress and the Nova Tech EEG (NTE) normative database demonstrated increased synchronized alpha and beta activity and less synchronized delta and theta activity in the dorsal anterior cingulate cortex in tinnitus patients with distress. It is interesting that the areas found show some overlap with the emotional component of the pain matrix and the distress related areas in asthmatic dyspnea. Unpleasantness of pain activates the anterior cingulate and prefrontal cortices, amygdala, and insula. As such, it might be that distress is related to alpha and beta activity in the dorsal anterior cingulate cortex, the amount of distress perceived to an alpha network consisting of the amygdala-anterior cingulate cortex-insula-parahippocampal area.

Tinnitus Intensity Dependent Gamma Oscillations of the Contralateral Auditory Cortex

Background Non-pulsatile tinnitus is considered a subjective auditory phantom phenomenon present in 10 to 15% of the population. Tinnitus as a phantom phenomenon is related to hyperactivity and reorganization of the auditory cortex. Magnetoencephalography studies demonstrate a correlation between gamma band activity in the contralateral auditory cortex and the presence of tinnitus. The present study aims to investigate the relation between objective gamma-band activity in the contralateral auditory cortex and subjective tinnitus loudness scores. Methods and Findings In unilateral tinnitus patients (N = 15; 10 right, 5 left) source analysis of resting state electroencephalographic gamma band oscillations shows a strong positive correlation with Visual Analogue Scale loudness scores in the contralateral auditory cortex (max r = 0.73, p<0.05). Conclusion Auditory phantom percepts thus show similar sound level dependent activation of the contralateral auditory cortex as observed in normal audition. In view of recent consciousness models and tinnitus network models these results suggest tinnitus loudness is coded by gamma band activity in the contralateral auditory cortex but might not, by itself, be responsible for tinnitus perception.

Burst Spinal Cord Stimulation: Toward Paresthesia-Free Pain Suppression

INTRODUCTIONSpinal cord stimulation is commonly used for neuropathic pain modulation. The major side effect is the onset of paresthesia. The authors describe a new stimulation design that suppresses pain as well as, or even better than, the currently used stimulation, but without creating paresthesia. METHODSA spinal cord electrode (Lamitrode) for neuropathic pain was implanted in 12 patients via laminectomy: 4 at the C2 level and 7 at the T8–T9 level for cervicobrachialgia and lumboischialgia, respectively (1 at T11 at another center). During external stimulation, the patients received the classic tonic stimulation (40 or 50 Hz) and the new burst stimulation (40-Hz burst with 5 spikes at 500 Hz per burst). RESULTSPain scores were measured using a visual analog scale and the McGill Short Form preoperatively and during tonic and burst stimulation. Paresthesia was scored as present or not present. Burst stimulation was significantly better for pain suppression, by both the visual analog scale score and the McGill Short Form score. Paresthesia was present in 92% of patients during tonic stimulation, and in only 17% during burst stimulation. Average follow-up was 20.5 months. CONCLUSIONThe authors present a new method of spinal cord stimulation using bursts that suppress neuropathic pain without the mandatory paresthesia. Pain suppression seems as good as or potentially better than that achieved with the currently used stimulation. Average follow-up after nearly 2 years (20.5 months) suggests that this stimulation design is stable.

The difference between uni- and bilateral auditory phantom percept.

OBJECTIVE Tinnitus can be considered an auditory phantom percept, in which patients hear an internal sound in the absence of any external sound source, mimicking tonal memory. Tinnitus however can be perceived exclusively uni- or bilaterally. METHODS The neurophysiological differences were investigated between unilateral and bilateral tinnitus using LORETA source localized resting state EEG recordings. RESULTS The difference between unilateral and bilateral tinnitus is reflected by high frequency activity (beta and gamma) in the superior prefrontal gurus, right parahippocampus, right angular gyrus and right auditory cortex. Unilateral tinnitus is characterized by contralateral beta2 in the superior prefrontal gyrus in comparison to bilateral tinnitus, but gamma in comparison to non-tinnitus subjects. Bilateral tinnitus has delta activity in the ventrolateral prefrontal cortex in comparison to unilateral tinnitus, and bilateral beta1 in comparison to non-tinnitus subjects. Bilateral tinnitus is also characterized by bilateral frontopolar beta1 activity. CONCLUSIONS Unilateral and bilateral tinnitus can be differentiated based on their resting state oscillation patterns: beta3 and gamma-band activity in the superior premotor cortex, parahippocampal area and angular gyrus seem to form the core of a spatial localization network involved in tinnitus. SIGNIFICANCE These differences should be taken into account when evaluating functional neuroimaging data relating to tinnitus.

Theta-gamma dysrhythmia and auditory phantom perception.

Tinnitus is considered an auditory phantom percept analogous to phantom pain. Thalamocortical dysrhythmia has been proposed as a possible pathophysiological mechanism for both tinnitus and pain. Thalamocortical dysrhythmia refers to a persistent pathological resting state theta-gamma coupling that is spatially localized at an area where normally alpha oscillations predominate. Auditory cortex stimulation via implanted electrodes has been developed to treat tinnitus, targeting an area of activation on functional MR imaging elicited by tinnitus-matched sound presentation. The authors describe a case in which clinical improvement was correlated with changes in intracranial recordings. Maximal tinnitus suppression was obtained by current delivery exactly at the blood oxygen level-dependent activation hotspot, which colocalizes with increased gamma and theta activity, in contrast to the other electrode poles, which demonstrated a normal alpha peak. These spectral changes normalized when stimulation induced tinnitus suppression, both on electrode and source-localized electroencephalography recordings. These data suggest that thetagamma coupling as proposed by the thalamocortical dysrhythmia model might be causally related to a conscious auditory phantom percept.

The Differences in Brain Activity between Narrow Band Noise and Pure Tone Tinnitus

Background Tinnitus is an auditory sensation characterized by the perception of sound or noise in the absence of any external sound source. Based on neurobiological research, it is generally accepted that most forms of tinnitus are attributable to maladaptive plasticity due to damage to auditory system. Changes have been observed in auditory structures such as the inferior colliculus, the thalamus and the auditory cortex as well as in non-auditory brain areas. However, the observed changes show great variability, hence lacking a conclusive picture. One of the reasons might be the selection of inhomogeneous groups in data analysis. Methodology The aim of the present study was to delineate the differences between the neural networks involved in narrow band noise and pure tone tinnitus conducting LORETA based source analysis of resting state EEG. Conclusions Results demonstrated that narrow band noise tinnitus patients differ from pure tone tinnitus patients in the lateral frontopolar (BA 10), PCC and the parahippocampal area for delta, beta and gamma frequency bands, respectively. The parahippocampal-PCC current density differences might be load dependent, as noise-like tinnitus constitutes multiple frequencies in contrast to pure tone tinnitus. The lateral frontopolar differences might be related to pitch specific memory retrieval.

Burst stimulation of the auditory cortex: a new form of neurostimulation for noise-like tinnitus suppression: Clinical article

OBJECT Tinnitus is an auditory phantom percept related to tonic and burst hyperactivity of the auditory system. Two parallel pathways supply auditory information to the cerebral cortex: the tonotopically organized lemniscal system, and the nontonotopic extralemniscal system, which fire in tonic and burst mode, respectively. Electrical cortex stimulation is a method capable of modulating activity of the human cortex by delivering stimuli in a tonic or burst way. Burst firing is shown to be more powerful in activating the cerebral cortex than tonic firing, and bursts may activate neurons that are not activated by tonic firing. METHODS Five patients with an implanted electrode on the auditory cortex were asked to rate their tinnitus distress and intensity on a visual analog scale before and after 40-Hz tonic and 40-Hz burst (5 pulses at 500 Hz) stimulation. All patients presented with both high-pitched pure tone and white noise components in their tinnitus. RESULTS A significantly better suppression for narrowband noise tinnitus with burst stimulation in comparison with tonic stimulation (Z = -2.03, p = 0.04) was found. For pure tone tinnitus, no difference was found between tonic and burst stimulation (Z = -0.58, p = 0.56). No significant effect was obtained for stimulation amplitude (Z = -1.21, p = 0.23) and electrical charge per pulse (Z = -0.67, p = 0.50) between tonic and burst stimulation. The electrical current delivery per second was significantly different (Z = -2.02, p = 0.04). CONCLUSIONS Burst stimulation is a new form of neurostimulation that might be helpful in treating symptoms that are intractable to conventional tonic stimulation. Further exploration of this new stimulation design is warranted.

Tinnitus in vascular conflict of the eighth cranial nerve: a surgical pathophysiological approach to ABR changes

Some forms of tinnitus are associated with a blood vessel being in close contact with the auditory nerve near its entrance into the brainstem. The outcome of operations for tinnitus, moving the blood vessel off the nerve (microvascular decompression operations, MVD) is less successful than microvascular decompression operations for other vascular conflict syndromes (hemifacial spasm, HFS, and trigeminal neuralgia, TGN). No generally accepted criteria exist for the selection of candidates for MVD for tinnitus. A pathophysiological approach for interpreting auditory brainstem response (ABR) changes is proposed as a basis for selection of tinnitus patients for the MVD operation. We followed changes in the ABR and the tinnitus in 78 patients with unilateral tinnitus, who had indications of having vascular conflicts of the eighth nerve. In 18 of these patients a blood vessel was removed of the auditory nerve and in 9 of these a correlation could be made between preoperative and postoperative clinical changes and ABR changes. In this retrospective study we found abnormalities in the amplitude of peak II and the interpeak latency (IPL) I-III of the ABR that were related to the duration of their tinnitus and its intensity. While no ABR changes could be detected during the first 2 years, after that period a decrease of the amplitude of peak II occurred, and a prolongation the IPL of peak I-III occurred in patients whose peak II had disappeared. The rate of IPL I-III increase slows down after 10 years. IPL I-III prolongation correlates with ipsilateral hearing loss at tinnitus frequency and worsens in time. This correlates with a worsening of the tinnitus associated with the worsening of the IPL I-III. Tinnitus frequency correlates to the frequency of maximal hearing loss and the more the hearing loss at tinnitus frequency the worse the tinnitus. Postoperative improvement of tinnitus correlated with postoperative improvement of peak II and postoperative improvement of hearing loss at the tinnitus frequency correlated with postoperative IPL I-III improvement. It is concluded that interpreting ABRs from a pathophysiological point of view can be beneficial for surgeons performing MVDs for tinnitus, especially with regard to timing of the surgery and interpretation of symptom presentation.

Microvascular decompression for tinnitus: significant improvement for tinnitus intensity without improvement for distress. A 4-year limit.

OBJECTIVEMicrovascular compressions of the cochlear nerve can lead to tinnitus. The tinnitus initially is related to nonsynchronous signal transmission in the auditory nerve, neurophysiologically characterized by a peak II amplitude decrease. Chronic compression can lead to a focal demyelination, resulting in an increase in Iinterpeak latency I-III with tinnitus and frequency-specific hearing loss as a consequence. Decompressing the cochlear nerve may result in improvement in tinnitus if the auditory nerve is not too damaged for recovery. The aim of the study is to find a cut-off point for this recovery based on clinical data. MATERIALS AND METHODSTwenty patients undergo a microvascular decompression of the vestibulocochlear nerve for unilateral intractable tinnitus. Pre- and postoperative visual analogue scale for tinnitus intensity and tinnitus questionnaires for tinnitus distress are analyzed before and after microvascular decompression. RESULTSOf the 20 patients studied, 10 had improvements on their tinnitus visual analogue score intensity postoperatively, 8 were unchanged, and 2 worsened. On the Tinnitus Questionnaire scores, 7 of 13 patients improved and 6 of the 13 patients worsened. If decompression is performed before the end of the 4th year of tinnitus duration, a significant tinnitus intensity improvement can be obtained (P < .05); after 4 years, improvement cannot be obtained (P = .55). However, the tinnitus distress does not seem to decrease significantly. CONCLUSIONMicrovascular decompression of the cochlear nerve can improve tinnitus intensity in selected patients if decompression is performed early, before the end of the 4th year. Tinnitus distress does not seem to change.