Brain networks involved in haptic and visual identification of facial expressions of emotion: An fMRI study

Previous neurophysiological and neuroimaging studies have shown that a cortical network involving the inferior frontal gyrus (IFG), inferior parietal lobe (IPL) and cortical areas in and around the posterior superior temporal sulcus (pSTS) region is employed in action understanding by vision and audition. However, the brain regions that are involved in action understanding by touch are unknown. Lederman et al. (2007) recently demonstrated that humans can haptically recognize facial expressions of emotion (FEE) surprisingly well. Here, we report a functional magnetic resonance imaging (fMRI) study in which we test the hypothesis that the IFG, IPL and pSTS regions are involved in haptic, as well as visual, FEE identification. Twenty subjects haptically or visually identified facemasks with three different FEEs (disgust, neutral and happiness) and casts of shoes (shoes) of three different types. The left posterior middle temporal gyrus, IPL, IFG and bilateral precentral gyrus were activated by FEE identification relative to that of shoes, regardless of sensory modality. By contrast, an inferomedial part of the left superior parietal lobule was activated by haptic, but not visual, FEE identification. Other brain regions, including the lingual gyrus and superior frontal gyrus, were activated by visual identification of FEEs, relative to haptic identification of FEEs. These results suggest that haptic and visual FEE identification rely on distinct but overlapping neural substrates including the IFG, IPL and pSTS region.     

Overlapping neural regions for processing rapid temporal cues in speech and nonspeech signals

Speech perception involves recovering the phonetic form of speech from a dynamic auditory signal containing both time-varying and steady-state cues. We examined the roles of inferior frontal and superior temporal cortex in processing these aspects of auditory speech and nonspeech signals. Event-related functional magnetic resonance imaging was used to record activation in superior temporal gyrus (STG) and inferior frontal gyrus (IFG) while participants discriminated pairs of either speech syllables or nonspeech tones. Speech stimuli differed in either the consonant or the vowel portion of the syllable, whereas the nonspeech signals consisted of sinewave tones differing along either a dynamic or a spectral dimension. Analyses failed to identify regions of activation that clearly contrasted the speech and nonspeech conditions. However, we did identify regions in the posterior portion of left and right STG and left IFG yielding greater activation for both speech and nonspeech conditions that involved rapid temporal discrimination, compared to speech and nonspeech conditions involving spectral discrimination. The results suggest that, when semantic and lexical factors are adequately ruled out, there is significant overlap in the brain regions involved in processing the rapid temporal characteristics of both speech and nonspeech signals.     

Selective attention modulates inferior frontal gyrus activity during action observation

Our ability to recognize the actions of others is subserved by a complex network of brain areas, including the inferior frontal gyrus (IFG), inferior parietal lobe (IPL) and superior temporal sulcus (STS). An unresolved issue is whether the activity within these regions requires top-down control or whether it arises relatively automatically during passive action observation. Here we used fMRI to determine whether cortical activity associated with action observation is modulated by the strategic allocation of selective attention. Participants observed moving and stationary images of reach-to-grasp hand actions, while they performed an attentionally demanding task at the fovea. We first defined regions-of-interest (ROIs) in the IFG, IPL and STS which responded to the perception of these actions. We then probed these ROIs while participants observed the identical, but now task-irrelevant, actions and instead performed an easy (low attentional load) or difficult (high attentional load) visual discrimination task. Our data indicate that the activity of the left IFG was consistently attenuated under conditions of high attentional load, while the remaining action observation areas remained relatively unaffected by attentional manipulations. The suppression of the left IFG was unique to the observation of hand actions, and did not occur during the observation of non-biological control stimuli, in the form of coherent dot motion. We propose that the left IFG is the site at which descending inhibitory processes affect the processing of observed actions, and that the attentional modulation of this region is responsible for filtering task-irrelevant actions during ongoing behavior.     

Towards a fronto-temporal neural network for the decoding of angry vocal expressions

Vocal expressions commonly elicit activity in superior temporal and inferior frontal cortices, indicating a distributed network to decode vocally expressed emotions. We examined the involvement of this fronto-temporal network for the decoding of angry voices during attention towards (explicit attention) or away from emotional cues in voices (implicit attention) based on a reanalysis of previous data (Frühholz, S., Ceravolo, L., Grandjean, D., 2012. Cerebral Cortex 22, 1107-1117). The general network revealed high interconnectivity of bilateral inferior frontal gyrus (IFG) to different bilateral voice-sensitive regions in mid and posterior superior temporal gyri. Right superior temporal gyrus (STG) regions showed connectivity to the left primary auditory cortex and secondary auditory cortex (AC) as well as to high-level auditory regions. This general network revealed differences in connectivity depending on the attentional focus. Explicit attention to angry voices revealed a specific right-left STG network connecting higher-level AC. During attention to a nonemotional vocal feature we also found a left-right STG network implicitly elicited by angry voices that also included low-level left AC. Furthermore, only during this implicit processing there was widespread interconnectivity between bilateral IFG and bilateral STG. This indicates that while implicit attention to angry voices recruits extended bilateral STG and IFG networks for the sensory and evaluative decoding of voices, explicit attention to angry voices solely involves a network of bilateral STG regions probably for the integrative recognition of emotional cues from voices.     

The Effect of Task Relevance on the Cortical Response to Changes in Visual and Auditory Stimuli: An Event-Related fMRI Study

Attention is, in part, a mechanism for identifying features of the sensory environment of potential relevance to behavior. The network of brain areas sensitive to the behavioral relevance of multimodal sensory events has not been fully characterized. We used event-related fMRI to identify brain regions responsive to changes in both visual and auditory stimuli when those changes were either behaviorally relevant or behaviorally irrelevant. A widespread network of "context-dependent" activations responded to both task-irrelevant and task-relevant events but responded more strongly to task-relevant events. The most extensive activations in this network were located in right and left temporoparietal junction (TPJ), with smaller activations in left precuneus, left anterior insula, left anterior cingulate cortex, and right thalamus. Another network of "context-independent" activations responded similarly to all events, regardless of task relevance. This network featured a large activation encompassing left supplementary and cingulate motor areas (SMA/CMA) as well as right IFG, right/left precuneus, and right anterior insula, with smaller activations in right/left inferior temporal gyrus and left posterior cingulate cortex. Distinct context-dependent and context-independent subregions of activation were also found within the left and right TPJ, left anterior insula, and left SMA/CMA. In the right TPJ, a subregion in the supramarginal gyrus showed sensitivity to the behavioral context (i.e., relevance) of stimulus changes, while two subregions in the superior temporal gyrus did not. The results indicate a role for the TPJ in detecting behaviorally relevant events in the sensory environment. The TPJ may serve to identify salient events in the sensory environment both within and independent of the current behavioral context.     

Inhibit yourself and understand the other: neural basis of distinct processes underlying Theory of Mind

Taking the perspective of somebody else (Theory of Mind; ToM) is an essential human ability depending on a large cerebral network comprising prefrontal and temporo-parietal regions. Recently, ToM was suggested to consist of two processes: (1) self-perspective inhibition and (2) belief reasoning. Moreover, it has been hypothesized that self-perspective inhibition may build upon basic motor response inhibition. This study tested both hypotheses for the first time using functional Magnetic Resonance Imaging (fMRI), through administering both a ToM and a stop-signal paradigm in the same subjects. Both self-perspective and motor response inhibition yielded bilateral inferior frontal gyrus (IFG) activation, suggesting a common inhibitory mechanism, while belief reasoning was mediated by the superior temporal gyrus (STG) and temporo-parietal junction (TPJ). Thus, we provide neurobiological evidence for a subdivision of ToM into self-perspective inhibition and belief reasoning. Furthermore, evidence for partially shared neural mechanisms for inhibition in complex social situations and basic motor response inhibition was found.     

Temporal correlation of spontaneous hemodynamic activity in language areas measured with functional near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS) was used to investigate resting state connectivity of language areas including bilateral inferior frontal gyrus (IFG) and superior temporal gyrus (STG). Thirty-two subjects participated in the experiment, including twenty adults and twelve children. Spontaneous hemodynamic fluctuations were recorded, and then intra- and inter-hemispheric temporal correlations of these signals were computed. The correlations of all hemoglobin components were observed significantly higher for adults than children. Moreover, the differences for the STG were more significant than for the IFG. In the adult group, differences in the correlations between males and females were not significant. Our results suggest by measuring resting state intra- and inter-hemispheric correlations, fNIRS is able to provide qualitative and quantitative evaluation on the functioning of the cortical network.OCIS codes: (170.2655) Functional monitoring and imaging, (170.3880) Medical and biological imaging, (170.5380) Physiology     

Prefrontal cortex involvement in preattentive auditory deviance detection: neuroimaging and electrophysiological evidence

Previous electrophysiological and neuroimaging studies suggest that the mismatch negativity (MMN) is generated by a temporofrontal network subserving preattentive auditory change detection. In two experiments we employed event-related brain potentials (ERP) and event-related functional magnetic resonance imaging (fMRI) to examine neural and hemodynamic activity related to deviance processing, using three types of deviant tones (small, medium, and large) in both a pitch and a space condition. In the pitch condition, hemodynamic activity in the right superior temporal gyrus (STG) increased as a function of deviance. Comparisons between small and medium and between small and large deviants revealed right prefrontal activation in the inferior frontal gyrus (IFG; BA 44/45) and middle frontal gyrus (MFG; BA 46), whereas large relative to medium deviants led to left and right IFG (BA 44/45) activation. In the ERP experiment the amplitude of the early MMN (90-120 ms) increased as a function of deviance, by this paralleling the right STG activation in the fMRI experiment. A U-shaped relationship between MMN amplitude and the degree of deviance was observed in a late time window (140-170 ms) resembling the right IFG activation pattern. In a subsequent source analysis constrained by fMRI activation foci, early and late MMN activity could be modeled by dipoles placed in the STG and IFG, respectively. In the spatial condition no reliable hemodynamic activation could be observed. The MMN amplitude was substantially smaller than in the pitch condition for all three spatial deviants in the ERP experiment. In contrast to the pitch condition it increased as a function of deviance in the early and in the late time window. We argue that the right IFG mediates auditory deviance detection in case of low discriminability between a sensory memory trace and auditory input. This prefrontal mechanism might be part of top-down modulation of the deviance detection system in the STG.     

Probabilistic fibre tract analysis of cytoarchitectonically defined human inferior parietal lobule areas reveals similarities to macaques

The human inferior parietal lobule (IPL) is a multimodal brain region, subdivided in several cytoarchitectonic areas which are involved in neural networks related to spatial attention, language, and higher motor processing. Tracer studies in macaques revealed differential connectivity patterns of IPL areas as the respective structural basis. Evidence for comparable differential fibre tracts of human IPL is lacking. Here, anatomical connectivity of five cytoarchitectonic human IPL areas to 64 cortical targets was investigated using probabilistic tractography. Connection likelihood was assessed by evaluating the number of traces between seed and target against the distribution of traces from that seed to voxels in the same distance as the target. The main fibre tract pattern shifted gradually from rostral to caudal IPL: Rostral areas were predominantly connected to somatosensory and superior parietal areas while caudal areas more strongly connected with auditory, anterior temporal and higher visual cortices. All IPL areas were strongly connected with inferior frontal, insular and posterior temporal areas. These results showed striking similarities with connectivity patterns in macaques, providing further evidence for possible homologies between these two species. This shift in fibre tract pattern supports a differential functional involvement of rostral (higher motor functions) and caudal IPL (spatial attention), with probable overlapping language involvement. The differential functional involvement of IPL areas was further supported by hemispheric asymmetries of connection patterns which showed left-right differences especially with regard to connections to sensorimotor, inferior frontal and temporal areas.     

The neural mechanism associated with the processing of onomatopoeic sounds

This event-related fMRI study was conducted to examine the blood-oxygen-level-dependent responses to the processing of auditory onomatopoeic sounds. We used a sound categorization task in which the participants heard four types of stimuli: onomatopoeic sounds, nouns (verbal), animal (nonverbal) sounds, and pure tone/noise (control). By discriminating between the categories of target sounds (birds/nonbirds), the nouns resulted in activations in the left anterior superior temporal gyrus (STG), whereas the animal sounds resulted in activations in the bilateral superior temporal sulcus (STS) and the left inferior frontal gyrus (IFG). In contrast, the onomatopoeias activated extensive brain regions, including the left anterior STG, the region from the bilateral STS to the middle temporal gyrus, and the bilateral IFG. The onomatopoeic sounds showed greater activation in the right middle STS than did the nouns and environmental sounds. These results indicate that onomatopoeic sounds are processed by extensive brain regions involved in the processing of both verbal and nonverbal sounds. Thus, we can posit that onomatopoeic sounds can serve as a bridge between nouns and animal sounds. This is the first evidence to demonstrate the way in which onomatopoeic sounds are processed in the human brain.     

Shared and distinct neural correlates of singing and speaking

Using a modified sparse temporal sampling fMRI technique, we examined both shared and distinct neural correlates of singing and speaking. In the experimental conditions, 10 right-handed subjects were asked to repeat intoned ("sung") and non-intoned ("spoken") bisyllabic words/phrases that were contrasted with conditions controlling for pitch ("humming") and the basic motor processes associated with vocalization ("vowel production"). Areas of activation common to all tasks included the inferior pre- and post-central gyrus, superior temporal gyrus (STG), and superior temporal sulcus (STS) bilaterally, indicating a large shared network for motor preparation and execution as well as sensory feedback/control for vocal production. The speaking more than vowel-production contrast revealed activation in the inferior frontal gyrus most likely related to motor planning and preparation, in the primary sensorimotor cortex related to motor execution, and the middle and posterior STG/STS related to sensory feedback. The singing more than speaking contrast revealed additional activation in the mid-portions of the STG (more strongly on the right than left) and the most inferior and middle portions of the primary sensorimotor cortex. Our results suggest a bihemispheric network for vocal production regardless of whether the words/phrases were intoned or spoken. Furthermore, singing more than humming ("intoned speaking") showed additional right-lateralized activation of the superior temporal gyrus, inferior central operculum, and inferior frontal gyrus which may offer an explanation for the clinical observation that patients with non-fluent aphasia due to left hemisphere lesions are able to sing the text of a song while they are unable to speak the same words.     

The human action recognition system and its relationship to Broca's area: an fMRI study

Primate studies have identified populations of neurons that are capable of action recognition. These "mirror neurons" show spiking activity both when the monkey executes or observes a grasping movement. These neurons are located in the ventral premotor cortex, possibly the homologue of "Broca's area" in human. This led to the speculation that action recognition and language production share a common system [Trends Neurosci. 21 (1998), 188]. To test this hypothesis, we combined an action recognition with a language production (VERB) and a grasping movement task (MOVE) by using functional magnetic resonance imaging. Action recognition-related activation was observed in the left inferior frontal gyrus and on the border between the inferior frontal gyrus and precentral gyrus (defined as IFG/PG), the ventral occipitotemporal junction, the superior and inferior parietal cortex, and in the intraparietal sulcus in the left hemisphere. An overlap of activations due to the language production, movement execution, and action recognition was found in the parietal cortex, the left inferior frontal gyrus, and the IFG-PG border (IFG/PG). The activation peaks of action recognition and verb generation were always different in single subjects, but no consistent spatial relationship was detected, in accord with the hypothesis that action recognition and language production share a common functional architecture.     

Differential cortical activation during voluntary and reflexive saccades in man

A saccade involves both a step in eye position and an obligatory shift in spatial attention. The traditional division of saccades into two types, the "reflexive" saccade made in response to an exogenous stimulus change in the visual periphery and the "voluntary" saccade based on an endogenous judgement to move gaze, is supported by lines of evidence which include the longer onset latency of the latter and the differential effects of lesions in humans and primates on each. It has been supposed that differences between the two types of saccade derive from differences in how the spatial attention shifts involved in each are processed. However, while functional imaging studies have affirmed the close link between saccades and attentional shifts by showing they activate overlapping cortical networks, attempts to contrast exogenous with endogenous ("covert") attentional shifts directly have not revealed separate patterns of cortical activation. We took the "overt" approach, contrasting whole reflexive and voluntary saccades using event-related fMRI. This demonstrated that, relative to reflexive saccades, voluntary saccades produced greater activation within the frontal eye fields and the saccade-related area of the intraparietal sulci. The reverse contrast showed reflexive saccades to be associated with relative activation of the angular gyrus of the inferior parietal lobule, strongest in the right hemisphere. The frequent involvement of the right inferior parietal lobule in lesions causing hemispatial neglect has long implicated this parietal region in an important, though as yet uncertain, role in the awareness and exploration of space. This is the first study to demonstrate preferential activation of an area in its posterior part, the right angular gyrus, during production of exogenously triggered rather than endogenously generated saccades, a finding which we propose is consistent with an important role for the angular gyrus in exogenous saccadic orienting.     

Distinct cortical networks for the detection and identification of human body

In the human brain information about bodies and faces is processed in specialized cortical regions named EBA and FBA (extrastriate and fusiform body area) and OFA and FFA (occipital and fusiform face area), respectively. Here we investigate with functional magnetic resonance imaging (fMRI) the cortical areas responsible for the identification of individual bodies and the distinction between ‘self’ and ‘others’. To this end we presented subjects with images of unfamiliar and familiar bodies and their own body. We identified separate coactivation networks for body-detection (processing body related information), body-identification (processing of information relating to individual bodies) and self-identification (distinction of self from others). Body detection involves the EBA in both hemispheres, and in the right hemisphere: the FBA and areas in the IPL (inferior parietal lobe). Body identification involves areas in the inferior frontal gyrus (IFG) of both hemispheres and in the right hemisphere areas in the medial frontal gyrus (MFG), in the cingulate gyrus (CG), in the central (CS) and the post-central sulcus (PCS), in the inferior parietal lobe (IPL) and the FBA. When the recognition of one's own body is contrasted to the identification of familiar bodies, differential activation is observed in areas of the inferior parietal lobe (IPL) and inferior parietal sulcus (IPS) of the right hemisphere, and in the posterior orbital gyrus (pOrbG) and in the lateral occipital gyrus (LOG) of the left hemisphere. Thus, identification of individual bodies and self-other distinction involve in addition to the classical occipito-parietal network a parieto-frontal network. Interestingly, the EBA shows no differential activation for distinctions between familiar or unfamiliar bodies or recognition of one's own body.     

复发性孤立性视神经炎患者初级视觉皮层功能连接的静息态fMRI

目的 采用静息态功能磁共振成像（rs-fMRI）技术,观察复发性孤立性视神经炎（RION）患者初级视觉皮层（V1）与全脑功能连接的改变。方法 收集45例RION患者（RION组）及45名年龄、性别相匹配的健康志愿者（正常对照组）的临床资料,并行常规头部MRI及rs-fMRI,选取V1为种子点,采用统计参数图5（SPM5）分析其与全脑的功能连接,比较两组数据的差异,并将RION组功能连接异常的脑区与其视力、病程及认知功能评分（PASAT）进行相关性分析。结果 与正常对照组相比,RION组左侧额中回、双侧枕叶舌回、右侧颞中回及右侧顶下小叶与V1的功能连接明显减低;双侧楔前叶、右侧额前回、左侧顶下小叶及右侧岛叶与V1的功能连接明显增强,且差异均有统计学意义（P均<0.01）。右侧顶下小叶及右侧额前回的功能连接异常与PASAT评分呈正相关;左侧额中回的功能连接异常与患者视力呈正相关。结论 rs-fMRI可检测出RION患者与V1区功能连接异常的脑区,并且显示与视力、病程及认知功能评分相关的脑区,可为临床探索RION功能连接异常提供客观依据。     

Task-dependent activations of human auditory cortex during spatial discrimination and spatial memory tasks

In the present study, we applied high-resolution functional magnetic resonance imaging (fMRI) of the human auditory cortex (AC) and adjacent areas to compare activations during spatial discrimination and spatial n-back memory tasks that were varied parametrically in difficulty. We found that activations in the anterior superior temporal gyrus (STG) were stronger during spatial discrimination than during spatial memory, while spatial memory was associated with stronger activations in the inferior parietal lobule (IPL). We also found that wide AC areas were strongly deactivated during the spatial memory tasks. The present AC activation patterns associated with spatial discrimination and spatial memory tasks were highly similar to those obtained in our previous study comparing AC activations during pitch discrimination and pitch memory (Rinne et al., 2009). Together our previous and present results indicate that discrimination and memory tasks activate anterior and posterior AC areas differently and that this anterior-posterior division is present both when these tasks are performed on spatially invariant (pitch discrimination vs. memory) or spatially varying (spatial discrimination vs. memory) sounds. These results also further strengthen the view that activations of human AC cannot be explained only by stimulus-level parameters (e.g., spatial vs. nonspatial stimuli) but that the activations observed with fMRI are strongly dependent on the characteristics of the behavioral task. Thus, our results suggest that in order to understand the functional structure of AC a more systematic investigation of task-related factors affecting AC activations is needed.     

Developmental changes in activation and effective connectivity in phonological processing

The current study examined developmental changes in activation and effective connectivity among brain regions during a phonological processing task, using fMRI. Participants, ages 9-15, were scanned while performing rhyming judgments on pairs of visually presented words. The orthographic and phonological similarity between words in the pair was independently manipulated, so that rhyming judgment could not be based on orthographic similarity. Our results show a developmental increase in activation in the dorsal part of left inferior frontal gyrus (IFG), accompanied by a decrease in the dorsal part of left superior temporal gyrus (STG). The coupling of dorsal IFG with other selected brain regions involved in the phonological decision increased with age, while the coupling of STG decreased with age. These results suggest that during development there is a shift from reliance on sensory auditory representations to reliance on phonological segmentation and covert articulation for performing rhyming judgment on visually presented words. In addition, we found a developmental increase in activation in left posterior parietal cortex that was not accompanied by a change in its connectivity with the other regions. These results suggest that maturational changes within a cortical region are not necessarily accompanied by an increase in its interactions with other regions and its contribution to the task. Our results are consistent with the idea that there is reduced reliance on primary sensory processes as task-relevant processes mature and become more efficient during development.     

In search of the hidden: an fMRI study with implications for the study of patients with autism and with acquired brain injury

The Embedded Figures Task involves a search for a target hidden in a more complex visual pattern. The task has been used to study local perception and visual search in a range of normal and pathological populations. After acquired brain damage, impairment on embedded figures is strongly associated with aphasia; in the context of developmental disorder, people with autism or with Asperger's syndrome are reliably found to be better than normal controls on the task. The current study employed functional MRI with healthy volunteers to elucidate the brain regions that are specifically involved in the local search aspects of the Embedded Figures Task. We did so by analyzing the neural activations that are implicated in the task over and above those involved in an easier visual search task and in a straightforward shape recognition task. Significant activations (P < 0.05, corrected) specific in the above sense to the Embedded Figures Task were found in left inferior and left superior parietal cortex and in left ventral premotor cortex (inferior frontal gyrus). By contrast, comparing the overall effect of visual search within geometric figures to pure recognition of geometric shapes revealed more widespread activations in parietal, occipital, cerebellar, and frontal areas bilaterally. The implications of these findings for some developmental and acquired pathologies of perceptual functioning are outlined. We also relate our results to studies of local/global processing in other tasks.     

How do we infer others' goals from non-stereotypic actions? The outcome of context-sensitive inferential processing in right inferior parietal and posterior temporal cortex

Humans permanently monitor others' behaviour and reason about their goals and intentions. Recent studies provided evidence suggesting that a very simple mechanism might underlie these functions. When observing stereotypic actions of others, goal inference seems to work through internal simulation of these actions in the self. However, less is known about the functional mechanisms and brain areas that are involved in inferring goals from others' actions when these actions are not stereotypic. Here we investigated the neural processes that are involved in goal inference processing of simple, non-stereotypic actions using functional brain imaging. We developed a paradigm in which we compared four simple finger lifting movements that differed in plausibility and intentionality as varied by action context. We found three regions that seem to be involved in goal inference processing of non-stereotypic implausible actions: (1) The superior temporal sulcus, (2) the right inferior parietal cortex, at the junction with the posterior temporal cortex (TPJ), and (3) the angular gyrus of the inferior parietal lobule. In line with teleological reasoning accounts of action understanding, inferring others' goals from non-stereotypic actions seems to be the outcome of context-sensitive inferential processing. In agreement with previous findings, we found the mirror system to be more strongly activated for intentionally produced actions [Iacoboni, M., Molnar-Szakacs, I., Gallese, V., Buccino, G., Mazziotta, J.C., Rizzolatti, G., 2005. Grasping the intentions of others with one's own mirror neuron system. PLoS Biol. 3, e79.], indicating an involvement of the IFG in representing intentional actions. Our findings support the idea that goal inference processing for non-stereotypic actions is primarily mediated by reasoning about action and context rather than by a direct mapping process via the mirror system.     

Action observation and mirror neuron network: a tool for motor stroke rehabilitation

Mirror neurons are a specific class of neurons that are activated and discharge both during observation of the same or similar motor act performed by another individual and during the execution of a motor act. Different studies based on non invasive neuroelectrophysiological assessment or functional brain imaging techniques have demonstrated the presence of the mirror neuron and their mechanism in humans. Various authors have demonstrated that in the human these networks are activated when individuals learn motor actions via execution (as in traditional motor learning), imitation, observation (as in observational learning) and motor imagery. Activation of these brain areas (inferior parietal lobe and the ventral premotor cortex, as well as the caudal part of the inferior frontal gyrus [IFG]) following observation or motor imagery may thereby facilitate subsequent movement execution by directly matching the observed or imagined action to the internal simulation of that action. It is therefore believed that this multi-sensory action-observation system enables individuals to (re) learn impaired motor functions through the activation of these internal action-related representations. In humans, the mirror mechanism is also located in various brain segment: in Broca's area, which is involved in language processing and speech production and not only in centres that mediate voluntary movement, but also in cortical areas that mediate visceromotor emotion-related behaviours. On basis of this finding, during the last 10 years various studies were carry out regarding the clinical use of action observation for motor rehabilitation of sub-acute and chronic stroke patients.