Distinct pathways involved in sound recognition and localization: a human fMRI study

Evidence from psychophysical studies in normal and brain-damaged subjects suggests that auditory information relevant to recognition and localization are processed by distinct neuronal populations. We report here on anatomical segregation of these populations. Brain activation associated with performance in sound identification and localization was investigated in 18 normal subjects using fMRI. Three conditions were used: (i) comparison of spatial stimuli simulated with interaural time differences; (ii) identification of environmental sounds; and (iii) rest. Conditions (i) and (ii) required acknowledgment of predefined targets by pressing a button. After coregistering, images were normalized and smoothed. Activation patterns were analyzed using SPM99 for individual subjects and for the whole group. Sound recognition and localization activated, as compared to rest, inferior colliculus, medial geniculate body, Heschl gyrus, and parts of the temporal, parietal, and frontal convexity bilaterally. The activation pattern on the fronto-temporo-parietal convexity differed in the two conditions. Middle temporal gyrus and precuneus bilaterally and the posterior part of left inferior frontal gyrus were more activated by recognition than by localization. Lower part of inferior parietal lobule and posterior parts of middle and inferior frontal gyri were more activated, bilaterally, by localization than by recognition. Regions selectively activated by sound recognition, but not those selectively activated by localization, were significantly larger in women. Passive listening paradigm revealed segregated pathways on superior temporal gyrus and inferior parietal lobule. Thus, anatomically distinct networks are involved in sound recognition and sound localization.     

Bilateral impairment of somesthetically mediated object recognition in humans

Thirty adult patients (six in each of five groups--neurologically normal, lacunar infarct-related hemiparesis, unilateral thalamic lacunar infarction, right cortical infarction with mild left hemineglect, and extensive right cortical infarction with severe left hemineglect) were asked to perform various tasks that encompassed basic and intermediate somatosensory functions and tactile and visual object recognition. Patients with thalamic and cortical infarctions had severe impairment of contralateral hand-mediated somatosensory functions in all three categories of somesthetic tasks, although patients with cortical infarction were more impaired on the object recognition task than were patients with thalamic infarction. Patients with extensive damage to the right hemisphere and severe left hemineglect also had impairment of somesthetically mediated object recognition in the ipsilateral hand despite normal basic and intermediate somatosensory function and visually mediated object recognition analogous to unilateral tactile agnosia. All other groups had normal ipsilateral tactile object recognition.     

Effects of unilateral brain damage on contralateral and ipsilateral upper extremity function in hemiplegia

This article describes the long-term effects of unilateral penetrating hemispheric lesions on contralateral and ipsilateral upper extremity motor performance and functional outcome. Activities-of-daily-living skill and gross motor performance contralateral to the lesions were compared among 32 left-sided and 19 right-sided hemiplegic subjects using analysis of variance and chi-square techniques. Ipsilateral to the damaged hemisphere, fine motor tasks of simple visual motor reaction time, grip and pinch strength, finger tapping, and Purdue Pegboard performance were tested. Analysis of covariance compared each ipsilateral task to performance in the corresponding hand of 70 matched controls. Results indicate similar long-term functional ADL outcome in right and left hemisphere-damaged subjects, despite more severe contralateral functional motor deficits following lesions of the left hemisphere. Right hemisphere lesions led to ipsilateral decrements in reaction time, and lesions of either hemisphere diminished grip or pinch strength, finger tapping, and pegboard performance ipsilaterally. These results demonstrate that unilateral brain damage involving the motor areas of either hemisphere has detrimental effects on ipsilateral upper extremity motor function. Findings are discussed and related to the concept that the left hemisphere is specialized or has greater neuronal representation for bilateral motor processes. Physical therapists involved in the treatment of patients with hemiplegia should be aware that motor functions of the ipsilateral, nonparetic upper extremity may also be affected adversely by unilateral brain lesions.     

Transcranial Doppler monitoring during language tasks in stroke patients with aphasia

Purpose. To investigate the pattern of hemispheric activation, according to cerebral blood flow changes, as measured by Transcranial Doppler Ultrasonography (TCD) during language tasks in stroke patients with aphasia.

Method. Prospective study investigating results of TCD monitoring during language naming and recognition tasks in ischemic stroke patients (n = 32) with and without aphasia and 5 control subjects.

Results. Delta mean flow velocity (MFV) in the left Middle Cerebral Artery (MCA) was found to be much lower in aphasia patients as compared to healthy subjects. Negative statistical correlation was found between the improvement of language ability and the blood flow velocity parameters in the left hemisphere. Aphasia patients with good language ability showed much higher MFV in the right MCA during the first test. Left hemispheric blood flow velocity shift was found to be higher during speech tasks in the patients with poor language ability.

Conclusions. Our study suggests that the performance of language tasks in aphasia patients during early recovery after stroke is associated with relatively high right hemisphere activation. High blood flow velocity in the right MCA of aphasia patients was found to be a good prognostic sign for better language ability. Arterial blood flow that shifted towards the left hemisphere during speech tasks was associated with poor language ability.     

利用fMRI和双手交替运动模式研究脑肿瘤所致的运动功能重组

目的应用fMRI研究双手交替运动模式下中央沟附近脑肿瘤患者运动功能重组的方式及特征.方法6名正常受试者和14名脑肿瘤患者采用双手交替对指运动模式行fMRI扫描,比较正常受试者与脑肿瘤患者脑激活的异同.结果正常人单手对指运动主要激活运动手对侧的大脑半球和同侧小脑半球.脑肿瘤患者非受累手运动所致的激活与正常受试者基本相同;而当受累手运动时,则出现运动功能的重组,包括肿瘤对侧正常半球内M1区的代偿性激活、肿瘤侧半球MI活动的减弱、双侧SMA等次级运动中枢激活区的增大以及双侧小脑半球的激活.结论采取双手交替运动模式,fMRI不仅显示了受累侧运动区的变形与移位,而且揭示了一种新的功能重组模式,即运动功能重组可能涉及分布于全脑的整个神经网络.     

Transcranial doppler monitoring during language tasks in stroke patients with aphasia

Purpose. To investigate the pattern of hemispheric activation, according to cerebral blood flow changes, as measured by Transcranial Doppler Ultrasonography (TCD) during language tasks in stroke patients with aphasia.

Method. Prospective study investigating results of TCD monitoring during language naming and recognition tasks in ischemic stroke patients (n = 32) with and without aphasia and 5 control subjects.

Results. Delta mean flow velocity (MFV) in the left Middle Cerebral Artery (MCA) was found to be much lower in aphasia patients as compared to healthy subjects. Negative statistical correlation was found between the improvement of language ability and the blood flow velocity parameters in the left hemisphere. Aphasia patients with good language ability showed much higher MFV in the right MCA during the first test. Left hemispheric blood flow velocity shift was found to be higher during speech tasks in the patients with poor language ability.

Conclusions. Our study suggests that the performance of language tasks in aphasia patients during early recovery after stroke is associated with relatively high right hemisphere activation. High blood flow velocity in the right MCA of aphasia patients was found to be a good prognostic sign for better language ability. Arterial blood flow that shifted towards the left hemisphere during speech tasks was associated with poor language ability.     

Cervical spinal cord BOLD fMRI study: modulation of functional activation by dexterity of dominant and non-dominant hands

The objective of this study was to investigate the effect of dexterity on the magnitude of signal changes in functional magnetic resonance imaging (fMRI) in the cervical spinal cord with unilateral finger-tapping. Right-handed healthy volunteers were investigated with blood oxygenation level-dependent (BOLD) fMRI. Spinal cord BOLD functional MR images were acquired from 10 healthy right-handed volunteers who performed four sessions of unilateral finger-tapping tasks: left sequential (LS), right sequential (RS), left interleaved (LI), and right interleaved (RI) tasks. Our results from the difficulty measurement test showed that finger-tapping in interleaved order was more difficult than in sequential order. For the functional activation, seven out of 10 subjects had activation in all four fMRI sessions (two of the subjects who showed no detectable activation had problems in volume registration). The mean contrast value of the activation area inside the entire cervical spinal cord was significantly higher in performing LS than RS tasks. The increase in the mean contrast value was because the less skilled and competent right hemisphere required additional processing power for doing the left hand task than the left hemisphere required in doing the right hand task. The analysis of the interleaved finger-tapping tasks did not show any significant difference in the results. This was probably because the interleaved task was similarly challenging for both hands, and required high dexterity. Therefore, differences in activity between the left and right hands were less apparent. Our results showed the modulation of activation intensity in the spinal cord by the dexterity.     

Where sound position influences sound object representations: a 7-T fMRI study

Evidence from human and non-human primate studies supports a dual-pathway model of audition, with partially segregated cortical networks for sound recognition and sound localisation, referred to as the What and Where processing streams. In normal subjects, these two networks overlap partially on the supra-temporal plane, suggesting that some early-stage auditory areas are involved in processing of either auditory feature alone or of both. Using high-resolution 7-T fMRI we have investigated the influence of positional information on sound object representations by comparing activation patterns to environmental sounds lateralised to the right or left ear. While unilaterally presented sounds induced bilateral activation, small clusters in specific non-primary auditory areas were significantly more activated by contra-laterally presented stimuli. Comparison of these data with histologically identified non-primary auditory areas suggests that the coding of sound objects within early-stage auditory areas lateral and posterior to primary auditory cortex AI is modulated by the position of the sound, while that within anterior areas is not.     

Neural correlates of relational and item-specific encoding during working and long-term memory in schizophrenia

Successful long-term memory (LTM) depends upon effective control of information in working memory (WM), and there is evidence that both WM and LTM are impaired by schizophrenia. This study tests the hypothesis that LTM deficits in schizophrenia may result from impaired control of relational processing in WM due to dorsolateral prefrontal cortex (DLPFC) dysfunction. fMRI was performed on 19 healthy controls and 20 patients with schizophrenia during WM tasks emphasizing relational (reorder trials) versus item-specific (rehearse trials) processing. WM activity was also examined with respect to LTM recognition on a task administered outside the scanner. Receiver operator characteristic analysis assessed familiarity and recollection components of LTM. Patients showed a disproportionate familiarity deficit for reorder versus rehearse trials against a background of generalized LTM impairments. Relational processing during WM led to DLPFC activation in both groups. However, this activation was less focal in patients than in controls, and patients with more severe negative symptoms showed less of a DLPFC increase. fMRI analysis of subsequent recognition performance revealed a group by condition interaction. High LTM for reorder versus rehearse trials was associated with bilateral DLPFC activation in controls, but not in patients who activated the left middle temporal and inferior occipital gyrus. Results indicate that although patients can activate the DLPFC on a structured relational WM task, this activation is less focal and does not translate to high retrieval success, suggesting a disruption in the interaction between WM and LTM processes in schizophrenia.     

单侧感音神经性耳聋病人听觉中枢的fMRI研究

目的探讨单侧感音神经性耳聋病人与正常听力者的听皮质频率敏感性排列结构的差异;双侧听皮质中枢半球优势的变化;单侧感音神经性耳聋病人皮层下区听觉传导通路的变化.方法20例正常志愿者和20例单侧感音神经性耳聋病人,分别采集T1WI、GRE-EPI及3D GRE T1WI影像.采用组块式方法分别随机给予500 Hz,4000 Hz两种纯音刺激,每种刺激重复2次.所有图像均经AFNI进行后处理,统计阈值概率设定为P＜10-5,激活范围阈值设定为半径5 mm,体积300 mm3的连续激活区域考虑为有意义激活区.结果正常听力者和单侧耳聋病人给予单耳500 Hz,4000 Hz刺激时,二者对于听皮质激活容积存在统计学差异(P＜0.05).正常听力者给予单耳刺激表现为对侧半球优势,半球激活容积比分别为7.56,6.02(右耳刺激);2.56,5.11(左耳刺激).而单侧耳聋病人则表现为同侧半球优势,半球激活容积比分别为0.62,0.69(左侧耳聋,右耳刺激);0.96,0.83(右侧耳聋,左耳刺激).结论正常听力者对500 Hz和4000 Hz的频率刺激激活区的位置存在差别.单侧感音神经性耳聋失去了听觉中枢的频率敏感性空间排列结构.单侧耳聋病人表现为同侧半球优势.500 Hz对正常听力者和单侧感音神经性耳聋病人的听皮质激活范围明显大于4000 Hz者.     

Impaired Visual Emotion Recognition After Minor Ischemic Stroke

ObjectiveTo assess the prevalence of impaired visual emotion recognition in patients who have experienced a minor ischemic stroke in the subacute phase and to determine associated factors of impaired visual emotion recognition.DesignA prospective observational study.SettingStroke unit of a teaching hospital.ParticipantsPatients with minor ischemic stroke (N=112).InterventionsNot applicable.Main Outcome MeasuresPatients with minor stroke underwent a neuropsychological assessment in the subacute phase for visual emotion recognition by the Ekman 60 Faces Test and for general cognition. Univariable linear regression analyses were performed to identify associated factors of emotion recognition impairment.ResultsIn 112 minor stroke patients, we found a prevalence of 25% of impaired visual emotion recognition. This was significantly correlated with impaired general cognition. Nevertheless, 10.9% of patients with normal general cognition still had impaired emotion recognition. Mood was negatively associated. Stroke localization, hemisphere side, and sex were not associated.ConclusionImpaired visual emotion recognition is found in about one-quarter of patients with minor ischemic stroke.     

Cognitive impairment after unilateral hemispheric injury of congenital or adult origin.

OBJECTIVE: The purpose of this study was to assess and compare cognitive functioning in adults with unilateral hemispheric injury due to either congenital damage or an ischemic event in young adulthood. METHOD: Adults with cerebral palsy resulting from left hemispheric brain damage were compared with adults who had a unilateral stroke in either the left or the right hemisphere. Our primary interest was to determine the impact on hemispheric dominance as revealed by dichotic listening, a task that assesses the bias for preferential listening and processing of sounds. Performance also was determined on a language-related task (word finding) and a spatial task (dot localization). RESULTS: Scores on the Quick Neurological Screening Test indicated that all participants demonstrated significant neuromotor deficits, whereas scores on the Barthel Index indicated that the participants were functional in basic activities of daily living. On cognitive assessments, healthy control participants demonstrated a pronounced left-hemisphere dominance and right-ear advantage; participants with injury to the left hemisphere showed a strong shift toward a right-hemisphere and left-ear dominance. In particular, injury of congenital origin appeared to foster this neural reorganization and localization of language-related functions into the healthy hemisphere. This shift was associated with a deterioration of performance on both the language and the spatial tasks. CONCLUSION: The importance of appreciating subtle deficits after unilateral injury is important in therapy. The dichotic listening test may provide a simple and useful means for evaluating persistent unilateral brain dysfunction in the clinical setting.     

Sex differences in the medial temporal lobe during encoding and recognition of pseudowords and abstract designs

Sex differences in various cognitive abilities have been demonstrated in terms of performance differentials and, more recently, in differences in activation patterns during fMRI. Hemispheric lateralization is sometimes accentuated in sex differences; e.g., women demonstrating greater activation of the left hemisphere than men during verbal tasks. We were interested in whether this phenomenon applies to memory for words and designs (i.e., material specific memory). Using analogous verbal (pseudowords) and nonverbal (abstract designs) encoding and recognition tasks completed back-to-back in a 3T scanner, we found that women tend to show exaggerated left hippocampal activation during certain stages of encoding and recognition of verbal information, compared with men. Likewise (although to a lesser extent), men showed more right hippocampal activation than women did during the abstract design learning task. These results have important implications for the generalization of fMRI memory study results, for example to clinical populations such as patients undergoing epilepsy surgery.     

Spatiotemporal patterns of language-specific brain activity in patients with chronic aphasia after stroke using magnetoencephalography

Six participants with chronic aphasia secondary to first-ever ischemic stroke within the middle cerebral artery (MCA) distribution of the left hemisphere and six neurologically intact controls of similar age were given a running recognition memory task for words while the magnetic flux normal to the scalp surface was measured with a whole-head neuromagnetometer. This task had been previously shown to be valid for the localization and lateralization of brain activity specific to receptive language function. As expected, patients exhibited relatively decreased activation in areas known to be involved in receptive language function, including superior temporal gyrus (STG) in the left hemisphere, as well as increased activation of areas outside of the left STG that might potentially support language function. Decreased activation within left STG was associated with a reduction in receptive language in patients, as was increased activation outside of left STG. Results support hypotheses suggesting that peri-lesional areas outside premorbid language areas may assume receptive language function after aphasia secondary to stroke, but that better recovery occurs when putative premorbid language areas are able to normalize.     

The functional neural architecture of components of attention in language-processing tasks

Using functional magnetic resonance imaging we examined three important dimensions of attentional control (selective attention, divided attention, and executive function) in 25 neurologically normal, right-handed men and women, using tasks involving the perception and processing of printed words, spoken words, or both. In the context of language-processing manipulations: selective attention resulted in increased activation at left hemisphere parietal sites as well as at inferior frontal sites, divided attention resulted in additional increases in activation at these same left hemisphere sites and was also uniquely associated with increased activation of homologous sites in the right hemisphere, and executive function (measured during a complex task requiring sequential decision-making) resulted in increased activation at frontal sites relative to all other conditions. Our findings provide support for the belief that specific functional aspects of attentional control in language processing involve widely distributed but distinctive cortical systems, with mechanisms associated with the control of perceptual selectivity involving primarily parietal and inferior frontal sites and executive function engaging specific sites in frontal cortex.     

Functional reorganization of brain in children affected with congenital hemiplegia: fMRI study

Using functional magnetic resonance imaging, the brain activation related to unilateral sequential finger-to-thumb opposition was studied in six children with a right congenital hemiplegia of cortical origin. They were compared to six age-matched controls. In the control group, movements with either hand asymmetrically activated the sensorimotor cortex and premotor areas in both cerebral hemispheres with a typical contralateral predominance. By contrast, paretic finger movements activated both hemispheres in the hemiplegic patients, with a strong ipsilateral predominance favoring the undamaged hemisphere. The activation induced by nonparetic finger movements was restricted to the contralateral undamaged hemisphere. Furthermore, the level of activation in the undamaged cortex was partly related to residual finger dexterity, according to covariance analysis. These activation patterns indicate an adaptive reorganization of the cortical motor networks in this group of patients, with a prominent involvement of the undamaged hemisphere in the control of finger movements with either hand.     

Deficits of Movement Accuracy and Proprioceptive Sense in the Ipsi-lesional Upper Limb of Patients with Hemiparetic Stroke

[Purpose] Previous studies have reported on motor deficits in the ipsilateral upper limbs (UL) of a damaged brain hemisphere in motor tasks. However, little is known about sensory deficits on the ipsilateral side. Therefore, we investigated whether both motor and sensory function of the ipsilateral UL are affected in patients with stroke. [Subjects and Methods] Fifty patients with unilateral stroke and 40 age- and sex- matched normal subjects participated in this study. Subjects were evaluated on performance of a tracking task for motor function, and by the joint reposition test for integrity of proprioceptive sense in the ipsilateral UL. [Result] The comparison of the stroke group and the control group showed significant differences in performance of the tracking task and the joint reposition test. The accuracy index for the tracking task showed significant correlation with the error score for the joint reposition test in the stroke group. [Conclusion] These results suggest that the ipsilateral UL of stroke patients has impairment in sensory function which is related to proprioceptive sense, along with motor deficits. Therefore, we think that the difficulty stroke patients experience with motor tasks for the ipsilateral UL is induced by diminished integrity of sensorimotor function due to both sensory and motor deficits.Key words: Visuomotor coordination, Proprioceptive sense, Motor deficits     

Ipsilateral motor cortex activation on functional magnetic resonance imaging during unilateral hand movements is related to interhemispheric interactions

Distal, unilateral hand movements can be associated with activation of both sensorimotor cortices on functional MRI. The neurophysiological significance of the ipsilateral activation remains unclear. We examined 10 healthy right-handed subjects with and without activation of the ipsilateral sensorimotor area during unilateral index-finger movements, to examine ipsilateral, uncrossed-descending pathways and interhemispheric interaction between bilateral motor areas, using transcranial magnetic stimulation (TMS). No subject showed ipsilateral activation during right hand movement. Five subjects showed ipsilateral sensorimotor cortical activation during left hand movement (IpsiLM1). In these subjects, paired-pulse TMS revealed a significant interhemispheric inhibition of the left motor cortex by the right hemisphere that was not present in the 5 subjects without IpsiLM1. Neither ipsilateral MEPs nor ipsilateral silent periods were evoked by TMS in any subjects. Our observation suggests that IpsiLM1 is not associated with the presence of ipsilateral uncrossed-descending projections. Instead, IpsiLM1 may reveal an enhanced interhemispheric inhibition from the right hemisphere upon the left to suppress superfluous, excessive activation.     

Orientation discrimination thresholds in migraine: a measure of visual cortical inhibition

Orientation discrimination is a visual task dependent on inhibitory mechanisms in the visual cortex. In this study, orientation discrimination thresholds for bar and grating patterns were measured at two visual field locations in subjects with migraine with (n = 20) and without aura (n = 20) and in migraine-free control subjects (n = 20). No statistically significant differences were found between migraine groups and the control group on either task at foveal or peripheral visual field locations. No significant correlations were found between psychophysical thresholds and age, total lifetime auras or total lifetime migraine episodes. However, a trend was seen toward slightly impaired performance on the two foveal tasks in a subgroup of subjects with the highest total lifetime aura count. Thus we have found no convincing evidence that impaired cortical inhibitory mechanisms are a predisposing characteristic in migraine, but cannot rule out the possibility that cortical inhibitory mechanisms may be adversely affected by repeated visual auras.