Bone conducted vibration selectively activates irregular primary otolithic vestibular neurons in the guinea pig

The main objective of this study was to determine whether bone-conducted vibration (BCV) is equally effective in activating both semicircular canal and otolith afferents in the guinea pig or whether there is preferential activation of one of these classes of vestibular afferents. To answer this question a large number (346) of single primary vestibular neurons were recorded extracellularly in anesthetized guinea pigs and were identified by their location in the vestibular nerve and classed as regular or irregular on the basis of the variability of their spontaneous discharge. If a neuron responded to angular acceleration it was classed as a semicircular canal neuron, if it responded to maintained roll or pitch tilts it was classified as an otolith neuron. Each neuron was then tested by BCV stimuli—either clicks, continuous pure tones (200–1,500 Hz) or short tone bursts (500 Hz lasting 7 ms)—delivered by a B-71 clinical bone-conduction oscillator cemented to the guinea pig's skull. All stimulus intensities were referred to that animal's own auditory brainstem response (ABR) threshold to BCV clicks, and the maximum intensity used was within the animal's physiological range and was usually around 70 dB above BCV threshold. In addition two sensitive single axis linear accelerometers cemented to the skull gave absolute values of the stimulus acceleration in the rostro-caudal direction. The criterion for a neuron being classed as activated was an audible, stimulus-locked increase in firing rate (a 10% change was easily detectable) in response to the BCV stimulus. At the stimulus levels used in this study, semicircular canal neurons, both regular and irregular, were insensitive to BCV stimuli and very few responded: only nine of 189 semicircular canal neurons tested (4.7%) showed a detectable increase in firing in response to BCV stimuli up to the maximum 2 V peak-to-peak level we delivered to the B-71 oscillator (which produced a peak-to-peak skull acceleration of around 6–8 g and was usually around 60–70 dB above the animal's own ABR threshold for BCV clicks). Regular otolithic afferents likewise had a poor response; only 14 of 99 tested (14.1%) showed any increase in firing rate up to the maximum BCV stimulus level. However, most irregular otolithic afferents (82.8%) showed a clear increase in firing rate in response to BCV stimuli: of the 58 irregular otolith neurons tested, 48 were activated, with some being activated at very low intensities (only about 10 dB above the animal's ABR threshold to BCV clicks). Most of the activated otolith afferents were in the superior division of the vestibular nerve and were probably utricular afferents. That was confirmed by evidence using juxtacellular injection of neurobiotin near BCV activated neurons to trace their site of origin to the utricular macula. We conclude there is a very clear preference for irregular otolith afferents to be activated selectively by BCV stimuli at low stimulus levels and that BCV stimuli activate some utricular irregular afferent neurons. The BCV generates compressional and shear waves, which travel through the skull and constitute head accelerations, which are sufficient to stimulate the most sensitive otolithic receptor cells.     

Vestibular primary afferent responses to sound and vibration in the guinea pig

This study tested whether air-conducted sound and bone-conducted vibration activated primary vestibular afferent neurons and whether, at low levels, such stimuli are specific to particular vestibular sense organs. In response to 500 Hz bone-conducted vibration or 500 Hz air-conducted sound, primary vestibular afferent neurons in the guinea pig fall into one of two categories--some neurons show no measurable change in firing up to 2 g peak-to-peak or 140 dB SPL. These are semicircular canal neurons (regular or irregular) and regular otolith neurons. In sharp contrast, otolith irregular neurons show high sensitivity: a steep increase in firing as stimulus intensity is increased. These sensitive neurons typically, but not invariably, were activated by both bone-conducted vibration and air-conducted sound, they originate from both the utricular and saccular maculae, and their sensitivity underpins new clinical tests of otolith function.     

Deactivation and activation of left frontal lobe during and after low-frequency repetitive transcranial magnetic stimulation over right prefrontal cortex: A near-infrared spectroscopy study

The effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) over the right frontal lobe on the function of the left frontal lobe were examined by near-infrared spectroscopy (NIRS) in eleven healthy subjects. rTMS applied 5 cm anterior to the motor cortex at 1 Hz and approximately 50% of the motor threshold intensity (MT) for 60 s resulted in a significantly larger decrease in the concentration of oxygenated hemoglobin ([oxy-Hb]) during the stimulation period followed by a significantly larger increase in [oxy-Hb] and a smaller decrease in the concentration of deoxygenated hemoglobin ([deoxy-Hb]) during the poststimulation baseline period than sham stimulation. These findings are interpreted as demonstrating the deactivation and activation of the left frontal cortex during and after rTMS of the right frontal cortex, respectively. If replicated in depressed patients, NIRS can be employed for monitoring rTMS effects as brain [Hb] changes in vivo, and may be helpful for determining therapeutic parameters of rTMS for individual patients.     

Brain resting state is disrupted in chronic back pain patients

Recent brain functional magnetic resonance imaging (fMRI) studies have shown that chronic back pain (CBP) alters brain dynamics beyond the feeling of pain. In particular, the response of the brain default mode network (DMN) during an attention task was found abnormal. In the present work similar alterations are demonstrated for spontaneous resting patterns of fMRI brain activity over a population of CBP patients (n = 12, 29–67 years old, mean = 51.2). Results show abnormal correlations of three out of four highly connected sites of the DMN with bilateral insular cortex and regions in the middle frontal gyrus (p < 0.05), in comparison with a control group of healthy subjects (n = 20, 21–60 years old, mean = 38.4). The alterations were confirmed by the calculation of triggered averages, which demonstrated increased coactivation of the DMN and the former regions. These findings demonstrate that CBP disrupts normal activity in the DMN even during the brain resting state, highlighting the impact of enduring pain over brain structure and function.     

上半规管良性阵发性位置性眩晕诊断试验分析和物理引擎耳石运动观察

目的 对上半规管良性阵发性位置性眩晕（BPPV）诊断试验进行分析，了解其诊断机制。方法 建立标准空间坐标系的膜迷路模型，设定膜迷路不同位置结石，基于物理引擎三维物理仿真，分析Dix Hallpike试验和仰卧悬挂头位试验耳石运动情况，进而推断所诱发眼震表现。结果 Dix-Hallpike试验和仰卧悬挂头位试验所有位置的结石都有一定程度的运动，并能诱发椭圆囊的结石经总管进入半规管。出现下跳眼震的情况，包括结石从椭圆囊进入后半规管，对侧后半规管结石向壶腹运动，上半规管的结石从壶腹嵴帽底部滑动到顶部，后者重复诊断实验仍为下跳眼震。重复10次观察，试验结果一致。结论 对于上半规管BPPV的诊断标准，还需要重新评估，观察眼震动态变化是必要的，其诊断方法需要改良。     

Dopamine D1 receptors and age differences in brain activation during working memory

In an fMRI study, 20 younger and 20 healthy older adults were scanned while performing a spatial working-memory task under two levels of load. On a separate occasion, the same subjects underwent PET measurements using the radioligand [¹¹C] SCH23390 to determine dopamine D₁ receptor binding potential (BP) in caudate nucleus and dorsolateral prefrontal cortex (DLPFC). The fMRI study revealed a significant load modulation of brain activity (higher load > lower load) in frontal and parietal regions for younger, but not older, adults. The PET measurements showed marked age-related reductions of D₁ BP in caudate and DLPFC. Statistical control of caudate and DLPFC D₁ binding eliminated the age-related reduction in load-dependent BOLD signal in left frontal cortex, and attenuated greatly the reduction in right frontal and left parietal cortex. These findings suggest that age-related alterations in dopaminergic neurotransmission may contribute to underrecruitment of task-relevant brain regions during working-memory performance in old age.     

Cortical areas related to performance of WAIS Digit Symbol Test: A functional imaging study

Many neuropsychological studies have shown that the Digit Symbol Test (DST) of the Wechsler Adult Intelligence Scale (WAIS) is useful for screening for dysfunctions of the brain. However, it remains unclear which brain areas are actually involved in the performance of DST and what brain functions are used for executing this test. In this study, we examined the cortical areas related to cognitive aspects of DST using functional magnetic resonance imaging (fMRI) and determined executive brain functions involved in this test on the basis of fMRI results. Eleven healthy young adults (mean = 21.6 years) performed a modified DST (mDST) task and its control task, which required a simple graphomotor response during fMRI data acquisition. The direct comparison of brain activations between the mDST task and the control task revealed greater activations in a fronto-parietal cortical network, including the bilateral inferior frontal sulci, left middle frontal gyrus (close to the frontal eye field) and left posterior parietal cortex. These activations are interpreted as reflecting the visual search process and/or the updating process of working memory during the mDST task execution. Furthermore, we found a positive correlation between the number of correct responses and activations in the bilateral inferior frontal regions, suggesting that these prefrontal areas have a crucial role in the performance of DST in a healthy young adult population.     

Alterations in regional homogeneity of resting-state brain activity in ketamine addicts

Ketamine is a non-competitive anatognist of the N-methyl-d-aspartate (NMDA) receptor commonly used as an anesthetic and analgesic. In sub-anesthetic doses, it can induce temporary psychotic symptoms and has served as a pharmacological model for schizophrenia. While its acute effects on brain and behavior have been studied, the effects of long-term exposure to ketamine on brain activity have been largely unexplored. In this study, we aimed to examine such effects on spontaneous brain dynamics measure using resting-state functional magnetic resonance imaging (fMRI). Forty-one patients with ketamine dependence and forty-four healthy control subjects were imaged with BOLD fMRI using a 3.0-Tesla Siemens scanner at the Magnetic Resonance Center of Hunan Provincial People's Hospital, analyzed with the regional homogeneity (ReHo) method. Compared with healthy controls, decreased ReHo was found in ketamine users in the right anterior cingulate cortex and increased ReHo was found in left precentral frontal gyrus (p < 0.05, cluster-level corrected). We also observed negative correlations between increased ReHo in precentral frontal gyrus and estimated total lifetime ketamine consumption and ketamine craving levels. To our knowledge, this is the first study the long-term effects of ketamine exposure on brain functional activity. Our findings indicate that ketamine dependence is associated with alterations in the functional connectivity of medial and lateral prefrontal cortices.     

外半规管良性阵发性位置性眩晕诊断试验分析和物理引擎耳石运动观察

目的对外半规管良性阵发性位置性眩晕(BPPV)诊断试验进行分析,了解其诊断机制。方法建立基于物理引擎三维物理仿真的BPPV迷路模型,设定外半规管不同位置结石,分析水平滚转试验过程不同位置耳石运动情况,进而可以推断所诱发眼震表现。结果水平滚转试验眼震表现形式多样,包括双侧背地眼震,可以判断为壶腹部结石和嵴帽结石,眼震弱侧为患侧;双侧向地眼震,可以判断为外半规管长臂侧结石,眼震强烈侧为患侧;一侧背地眼震一侧向地眼震,考虑长臂侧壶腹部结石;水平滚转试验存在的设计缺陷是会导致耳石复位,影响诊断试验的敏感性。10次重复试验结果一致。结论60°水平滚转试验有效修正了90°水平滚转试验存在的缺陷。基于物理引擎对诊断试验进行分析,对于我们理解外半规管BPPV的诊断机制有重要意义,也有助于改良和创新诊断方法。     

Brain regions concerned with perceptual skills in tennis: an fMRI study.

Sporting performance makes special demands on perceptual skills, but the neural mechanisms underlying such performance are little understood. We address this issue, making use of fMRI to identify the brain areas activated in viewing and responding to video sequences of tennis players, filmed from the opponent's perspective. In a block-design, fMRI study, 9 novice tennis players watched video clips of tennis play. The main stimulus conditions were (1) serve sequences, (2) non-serve behaviour (ball bouncing) and (3) static control sequences. A button response was required indicating the direction of serve (left or right for serve sequences, middle button for non-serve and static sequences). By comparing responses to the three stimulus conditions, it was possible to identify two groups of brain regions responsive to different components of the task. Areas MT/MST and STS in the posterior part of the temporal lobe responded either to serve and to non-serve stimuli, relative to static controls. Serve sequences produced additional regions of activation in the parietal lobe (bilateral IPL, right SPL) and in the right frontal cortex (IFGd, IFGv), and these areas were not activated by non-serve sequences. These regions of the parietal and frontal cortex have been implicated in a "mirror neuron" network in the human brain. It is concluded that the task of judgement of serve direction produces two different patterns of response: activations in the MT/MST and STS concerned with primarily with the analysis of motion and body actions, and activations in the parietal and frontal cortex associated specifically with the task of identification of direction of serve.     

Position and velocity responses to galvanic vestibular stimulation in human subjects during standing

Galvanic vestibular stimulation (GVS) in animals modulates the firing of otolith and semicircular canal afferents alike. Here, we look for postural responses evoked by GVS from the otolith organs and semicircular canals. To minimise the modifying effects of somatosensory input on the response, low-intensity (0.3–0.5 mA) GVS was applied for 8 s while subjects stood on foam rubber with the feet together and strapped to the floor. The response had three phases: (i) a rapid movement during the first second, (ii) a slower movement that persisted throughout the stimulus, and (iii) a rapid partial return movement after GVS stopped. The three movement velocities were significantly different. The GVS response therefore appears to be the sum of a step response that returns to the starting point when the stimulus stops, and a constant-velocity ramp response for the duration of the stimulus without a return movement. Subjects' responses differed in size and profile, some with the step or ramp responses almost exclusively but most with a combination of both. The 'step-plus-ramp' model was tested by comparing the three velocities. If the responses add, the initial velocity should not be different from the sum of the velocities during the ramp-only period and the step-only period at offset. ANOVA and pairwise comparisons confirmed this. It is concluded that postural responses to GVS arise through stimulation of both otolith and canal afferents.     

威胁性情绪面孔对正常人脑的激活模式

目的:探讨正常人脑对威胁性情绪面孔的反应模式。方法:以愤怒和恐惧面孔为情绪刺激,在34名健康志愿受试者完成情绪面孔匹配任务的同时利用功能磁共振成像(fMRI)技术进行全脑数据采集。用SPM 8等软件处理功能成像数据,分析威胁性情绪面孔的脑区激活。结果:与威胁性情绪面孔视觉刺激加工相关的脑区主要分布在额叶皮质、颞叶、左侧杏仁核等,楔叶、枕叶等与视觉刺激相关脑区也有显著激活。结论:威胁性情绪面孔刺激对正常人脑的激活主要表现为左侧杏仁核、额叶、颞叶等多个脑区的协同加工机制。     

Reduced serum non-enzymatic antioxidant defense and increased lipid peroxidation in schizophrenic patients on a hypocaloric diet

This study aimed to affirm the use of functional near-infrared spectroscopy (fNIR) in examining frontal lobe role during automatic (i.e., requires retrieval from long-term memory) and method-based (i.e., requires calculation) arithmetic processing. Adult university students (math difficulties [MD] and control) performed simple arithmetic calculations while monitored using an fNIR system designed to image regions within the frontal cortices. Addition and subtraction problems presented on a computer screen belonged to one of three categories: triples “under 10” (e.g., 2 + 3 = ?, 5 − 3 = ?), triples that “break 10” (e.g., 5 + 8 = ?, 13 − 5 = ?), or triples “including 10” (e.g., 10 + 7 = ?, 17 − 10 = ?). fNIR recordings indicated significant interactions between type of triple, operation, and group over left frontal lobe, and between type of triple and group over right frontal lobe.Within-group differences among controls were found in the “break 10” triples with higher DeOxyHb level recorded during subtraction processing. Between-group differences were found in the “break 10” and “including 10” triples for subtraction with higher levels of DeOxyHb recorded among controls. Results imply that among adults frontal lobe is still involved during simple mathematical processing and fNIR recordings can differentiate its role in adults of varying mathematical ability.     

Laterality effect on emotional faces processing: ALE meta-analysis of evidence

Recognizing emotion from facial expressions draws on diverse psychological processes implemented in a large array of neural structures. Two major theories of cerebral lateralization of emotional perception have been proposed: (i) the Right-Hemisphere Hypothesis (RHH) and (ii) the Valence-Specific Hypothesis (VSH). To test these lateralization models we conducted a large voxel-based meta-analysis of current functional magnetic resonance imaging (fMRI) studies employing emotional faces paradigms in healthy volunteers. Two independent researchers conducted separate comprehensive PUBMED (1990–May 2008) searches to find all functional magnetic resonance imaging studies using a variant of the emotional faces paradigm in healthy subjects. Out of the 551 originally identified studies, 105 studies met inclusion criteria. The overall database consisted of 1785 brain coordinates which yield an overall sample of 1600 healthy subjects. We found no support for the hypothesis of overall right-lateralization of emotional processing. Conversely, across all emotional conditions the parahippocampal gyrus and amygdala, fusiform gyrus, lingual gyrus, precuneus, inferior and middle occipital gyrus, posterior cingulated, middle temporal gyrus, inferior frontal and superior frontal gyri were activated bilaterally (p = 0.001). There was a valence-specific lateralization of brain response during negative emotions processing in the left amygdala (p = 0.001). Significant interactions between the approach and avoidance dimensions and prefrontal response were observed (p = 0.001).     

The contribution of the horizontal semicircular canals to the response to off-vertical-axis rotation in the cat

Summary The response to off-vertical-axis rotation (OVAR) was measured in cats under circumstances in which the signals from the horizontal semicircular canals and otoliths were opposed. Opposition was achieved by sudden acceleration or deceleration during constant velocity OVAR. The degree of opposition was expressed as a canal/otolith ratio where a ratio of unity indicated agreement. For a canal/otolith ratio of 1, the OVAR gain (eye velocity/ stimulus velocity) was 0.73 (±0.13). The steady-state OVAR response was, however, reduced if the canals and otoliths were opposed. The reduction depended on the degree of opposition with a fall-off of 0.15 gain/(unit of canal/otolith ratio). These findings are discussed with respect to the central velocity store and the mechanism underlying the generation of the OVAR response.     

Patterns of canal and otolith afferent input convergence in frog second-order vestibular neurons

Second-order vestibular neurons (2 degrees VN) were identified in the isolated frog brain by the presence of monosynaptic excitatory postsynaptic potentials (EPSPs) after separate electrical stimulation of individual vestibular nerve branches. Combinations of one macular and the three semicircular canal nerve branches or combinations of two macular nerve branches were stimulated separately in different sets of experiments. Monosynaptic EPSPs evoked from the utricle or from the lagena converged with monosynaptic EPSPs from one of the three semicircular canal organs in ~30% of 2 degrees VN. Utricular afferent signals converged predominantly with horizontal canal afferent signals (74%), and lagenar afferent signals converged with anterior vertical (63%) or posterior vertical (37%) but not with horizontal canal afferent signals. This convergence pattern correlates with the coactivation of particular combinations of canal and otolith organs during natural head movements. A convergence of afferent saccular and canal signals was restricted to very few 2 degrees VN (3%). In contrast to the considerable number of 2 degrees VN that received an afferent input from the utricle or the lagena as well as from one of the three canal nerves (~30%), smaller numbers of 2 degrees VN (14% of each type of 2 degrees otolith or 2 degrees canal neuron) received an afferent input from only one particular otolith organ or from only one particular semicircular canal organ. Even fewer 2 degrees VN received an afferent input from more than one semicircular canal or from more than one otolith nerve (~7% each). Among 2 degrees VN with afferent inputs from more than one otolith nerve, an afferent saccular nerve input was particularly rare (4-5%). The restricted convergence of afferent saccular inputs with other afferent otolith or canal inputs as well as the termination pattern of saccular afferent fibers are compatible with a substrate vibration sensitivity of this otolith organ in frog. The ascending and/or descending projections of identified 2 degrees VN were determined by the presence of antidromic spikes. 2 degrees VN mediating afferent utricular and/or semicircular canal nerve signals had ascending and/or descending axons. 2 degrees VN mediating afferent lagenar or saccular nerve signals had descending but no ascending axons. The latter result is consistent with the absence of short-latency macular signals on extraocular motoneurons during vertical linear acceleration. Comparison of data from frog and cat demonstrated the presence of a similar organization pattern of maculo- and canal-ocular reflexes in both species.     

Low dietary sodium is anxiogenic in rats

Noise exposure during the critical period of postnatal development in rats results in anomalous processing of acoustic stimuli in the adult auditory system. In the present study, the behavioral consequences of an acute acoustic trauma in the critical period are assessed in adult rats using the acoustic startle reflex (ASR) and prepulse inhibition (PPI) of ASR. Rat pups (strain Long-Evans) were exposed to broad-band noise of 125 dB SPL for 8 min on postnatal day 14; at the age of 3-5 months, ASR and PPI of ASR were examined and compared with those obtained in age-matched controls. In addition, hearing thresholds were measured in all animals by means of auditory brainstem responses. The results show that although the hearing thresholds in both groups of animals were not different, a reduced strength of the startle reflex was observed in exposed rats compared with controls. The efficacy of PPI in exposed and control rats was also markedly different. In contrast to control rats, in which an increase in prepulse intensity was accompanied by a consistent increase in the efficacy of PPI, the PPI function in the exposed animals was characterized by a steep increase in inhibitory efficacy at low prepulse intensities of 20-30 dB SPL. A further increase of prepulse intensity up to 60-70 dB SPL caused only a small and insignificant change of PPI. Our findings demonstrate that brief noise exposure in rat pups results in altered behavioral responses to sounds in adulthood, indicating anomalies in intensity coding and loudness perception.     

Evidence for a dysfunctional retrosplenial cortex in patients with schizophrenia: a functional magnetic resonance imaging study with a semantic-perceptual contrast

We investigated whether the retrosplenial and the posterior cingulate cortex (RS-PCC) is functionally impaired in schizophrenia patients. Therefore, we measured functional magnetic resonance imaging (fMRI) signal changes associated with a synonym-judgment task known to activate, among other areas, the RS-PCC. Compared to 12 matched control subjects, 12 schizophrenia patients exhibited reliably weaker activations in the RS-PCC, the dorsolateral prefrontal cortex and the left orbitofrontal cortex (P < 0.05, corrected). Differences in frontal activations are in line with previous studies showing a structurally and functionally affected prefrontal cortex in schizophrenia. The impaired RS-PCC functionality in a semantic task may relate to verbal memory deficits frequently observed in schizophrenia patients, because this region is pivotal for gating information into the medial temporal lobe memory system.     

Otolith and canal reflexes in human standing

We used galvanic vestibular stimulation (GVS) to identify human balance reflexes of the semicircular canals and otolith organs. The experiment used a model of vestibular signals arising from GVS modulation of the net signal from vestibular afferents. With the head upright, the model predicts that the GVS-evoked canal signal indicates lateral head rotation while the otolith signal indicates lateral tilt or acceleration. Both signify body sway transverse to the head. With the head bent forward, the model predicts that the canal signal indicates body spin about a vertical axis but the otolith signal still signifies lateral body motion. Thus, we compared electromyograms (EMG) in the leg muscles and body sway evoked by GVS when subjects stood with the head upright or bent forward. With the head upright, GVS evoked a large sway in the direction of the anodal electrode. This response was abolished with the head bent forward leaving only small, oppositely directed, transient responses at the start and end of the stimulus. With the head upright, GVS evoked short-latency (60–70 ms), followed by medium-latency (120 ms) EMG responses, of opposite polarity. Bending the head forward abolished the medium-latency but preserved the short-latency response. This is compatible with GVS evoking separate otolithic and canal reflexes, indicating that balance is controlled by independent canal and otolith reflexes, probably through different pathways. We propose that the short-latency reflex and small transient sway are driven by the otolith organs and the medium-latency response and the large sway are driven by the semicircular canals.