RESUMEN
Mental imitation, perhaps a precursor to motor imitation, involves visual perspective-taking and motor imagery. Research on mental imitation in autism spectrum disorders (ASD) has been rather limited compared to that on motor imitation. The main objective of this fMRI study is to determine the differences in brain responses underlying mirroring and mentalizing networks during mental imitation in children and adolescents with ASD. Thirteen high-functioning children and adolescents with ASD and 15 age-and- IQ-matched typically developing (TD) control participants took part in this fMRI study. In the MRI scanner, participants were shown cartoon pictures of people performing everyday actions (Transitive actions: e.g., ironing clothes but with the hand missing; and Intransitive actions: e.g., clapping hands with the palms missing) and were asked to identify which hand or palm orientation would best fit the gap. The main findings are: 1) both groups performed equally while processing transitive and intransitive actions; 2) both tasks yielded activation in the bilateral inferior frontal gyrus (IFG) and inferior parietal lobule (IPL) in ASD and TD groups; 3) Increased activation was seen in ASD children, relative to TD, in left ventral premotor and right middle temporal gyrus during intransitive actions; and 4) ASD symptom severity positively correlated with activation in left parietal, right middle temporal, and right premotor regions across all subjects. Overall, our findings suggest that regions mediating mirroring may be recruiting more brain resources in ASD and may have implications for understanding social movement through modeling.
Asunto(s)
Trastorno del Espectro Autista/fisiopatología , Encéfalo/fisiopatología , Conducta Imitativa/fisiología , Actividad Motora/fisiología , Percepción Social , Percepción Visual/fisiología , Adolescente , Trastorno del Espectro Autista/diagnóstico por imagen , Encéfalo/diagnóstico por imagen , Mapeo Encefálico , Niño , Conducta Infantil/fisiología , Femenino , Mano/fisiología , Humanos , Imagen por Resonancia Magnética , Masculino , Neuronas Espejo , Vías Nerviosas/diagnóstico por imagen , Vías Nerviosas/fisiopatología , Pruebas Neuropsicológicas , Índice de Severidad de la EnfermedadRESUMEN
While deficits in imitation had been reported in children with autism spectrum disorder (ASD), its exact nature remains unclear. A dysfunction in mirroring mechanisms (through action imitation) has been proposed by some studies to explain this, although some recent evidence points against this hypothesis. The current study used behavior and functional MRI to examine the integrated functioning of the regions that are considered part of the Action Imitation network (AIN) in children and adolescents with ASD during a motor imitation task. Fourteen ASD and 15 age-and-IQ-matched typically developing (TD) children were asked to imitate a series of hand gestures in the MRI scanner. Intact performance on imitation (accurate imitation of hand gestures outside the scanner) in both ASD and TD groups was accompanied by significantly lower activity in ASD participants, relative to TD, in right angular gyrus, precentral gyrus, and left middle cingulate. In addition, autism traits were found to be significantly correlated with activation in the right angular gyrus. Overall, the findings of this study support the role of AIN in imitation and a potential difference in the recruitment of this network in ASD children.
Asunto(s)
Trastorno del Espectro Autista/fisiopatología , Encéfalo/fisiopatología , Gestos , Conducta Imitativa/fisiología , Destreza Motora/fisiología , Adolescente , Trastorno del Espectro Autista/diagnóstico por imagen , Trastorno del Espectro Autista/psicología , Trastorno Autístico/diagnóstico por imagen , Trastorno Autístico/fisiopatología , Trastorno Autístico/psicología , Encéfalo/diagnóstico por imagen , Mapeo Encefálico , Niño , Femenino , Humanos , Pruebas de Inteligencia , Imagen por Resonancia Magnética , Masculino , Vías Nerviosas/diagnóstico por imagen , Vías Nerviosas/fisiopatología , Pruebas NeuropsicológicasRESUMEN
Appropriate interpretation of figurative language involves inferring the speaker's intent by integrating word meaning with context. In disorders like autism, understanding intended and contextual meanings in language may pose a challenge. Such difficulties are prevalent even when individuals exhibit otherwise fluent language ability (Szatmari et al., 1990). A pun is a rhetorical technique in which a speaker deliberately invokes multiple meanings through a word or phrase likely resulting in a joke. Comprehending puns may involve identifying multiple meanings of a word, embedding it in right contexts, and understanding the underlying humor. This fMRI study investigated the brain responses associated with figures of speech like puns. In the fMRI scanner, participants read sentences containing puns (e.g. To write with a broken pencil is pointless) and control sentences (literal meaning) presented in a blocked design format. The participants' task was to silently read and understand one meaning (in the literal condition) or two meanings (in the pun condition). Participants with autism, relative to typical controls, showed an increase in overall activation while comprehending sentences containing puns, particularly within the right hemisphere as well as in relatively posterior brain areas. Overall, there was reduced response in left hemisphere areas, reduced response to humor, and more distributed recruitment of regions in autism relative to control participants. We also examined the relationship between symptom severity in autism and verbal ability with brain responses to pun comprehension finding negative and positive correlations respectively. Overall, the results from the present study suggest that individuals with autism resort to altered neural routes in comprehending language in general, and figurative language in particular.
Asunto(s)
Trastorno Autístico/fisiopatología , Corteza Cerebral/fisiopatología , Comprensión , Lateralidad Funcional , Percepción del Habla , Ingenio y Humor como Asunto , Adolescente , Adulto , Femenino , Humanos , Masculino , Adulto JovenRESUMEN
Newly emerging theories suggest that the brain does not function as a cohesive unit in autism, and this discordance is reflected in the behavioral symptoms displayed by individuals with autism. While structural neuroimaging findings have provided some insights into brain abnormalities in autism, the consistency of such findings is questionable. Functional neuroimaging, on the other hand, has been more fruitful in this regard because autism is a disorder of dynamic processing and allows examination of communication between cortical networks, which appears to be where the underlying problem occurs in autism. Functional connectivity is defined as the temporal correlation of spatially separate neurological events. Findings from a number of recent fMRI studies have supported the idea that there is weaker coordination between different parts of the brain that should be working together to accomplish complex social or language problems. One of the mysteries of autism is the coexistence of deficits in several domains along with relatively intact, sometimes enhanced, abilities. Such complex manifestation of autism calls for a global and comprehensive examination of the disorder at the neural level. A compelling recent account of the brain functioning in autism, the cortical underconnectivity theory, provides an integrating framework for the neurobiological bases of autism. The cortical underconnectivity theory of autism suggests that any language, social, or psychological function that is dependent on the integration of multiple brain regions is susceptible to disruption as the processing demand increases. In autism, the underfunctioning of integrative circuitry in the brain may cause widespread underconnectivity. In other words, people with autism may interpret information in a piecemeal fashion at the expense of the whole. Since cortical underconnectivity among brain regions, especially the frontal cortex and more posterior areas, has now been relatively well established, we can begin to further understand brain connectivity as a critical component of autism symptomatology. A logical next step in this direction is to examine the anatomical connections that may mediate the functional connections mentioned above. Diffusion Tensor Imaging (DTI) is a relatively novel neuroimaging technique that helps probe the diffusion of water in the brain to infer the integrity of white matter fibers. In this technique, water diffusion in the brain is examined in several directions using diffusion gradients. While functional connectivity provides information about the synchronization of brain activation across different brain areas during a task or during rest, DTI helps in understanding the underlying axonal organization which may facilitate the cross-talk among brain areas. This paper will describe these techniques as valuable tools in understanding the brain in autism and the challenges involved in this line of research.
Asunto(s)
Trastorno Autístico/fisiopatología , Encéfalo/fisiopatología , Imagen de Difusión Tensora/métodos , Imagen por Resonancia Magnética/métodos , Trastorno Autístico/patología , Encéfalo/anatomía & histología , Niño , HumanosRESUMEN
The ability to conceptualize and manipulate tools in a complex manner is a distinguishing characteristic of humans, and forms a promising milestone in human evolution. While using tools is a motor act, proposals for executing such acts may be evoked by the mere perception of a tool. Imagining an action using a tool may invoke mental readjustment of body posture, planning motor movements, and matching such plans with the model action. This fMRI study examined the brain response in 32 healthy adults when they either viewed a tool or imagined using it. While both viewing and imagining tasks recruited similar regions, imagined tool use showed greater activation in motor areas, and in areas around the bilateral temporoparietal junction. Viewing tools, on the other hand, produced robust activation in the inferior frontal, occipital, parietal, and ventral temporal areas. Analysis of gender differences indicated males recruiting medial prefrontal and anterior cingulate cortices and females, left supramarginal gyrus and left anterior insula. While tool viewing seems to generate prehensions about using them, the imagined action using a tool mirrored brain responses underlying functional use of it. The findings of this study may suggest that perception and imagination of tools may form precursors to overt actions.
Asunto(s)
Encéfalo/fisiología , Imaginación/fisiología , Percepción/fisiología , Comportamiento del Uso de la Herramienta/fisiología , Adolescente , Adulto , Corteza Cerebral/fisiología , Cognición/fisiología , Interpretación Estadística de Datos , Femenino , Fijación Ocular/fisiología , Lateralidad Funcional/fisiología , Humanos , Procesamiento de Imagen Asistido por Computador , Pruebas de Inteligencia , Aprendizaje/fisiología , Imagen por Resonancia Magnética , Masculino , Pruebas Neuropsicológicas , Caracteres Sexuales , Adulto JovenRESUMEN
Although several studies suggest an imitation deficit as a key feature of autism, questions have been raised about the consistency of this finding and about the component skills involved in imitation. The primary aim of this review is to examine the uneven profile of imitation deficits found in autism in the context of the mirror neuron system (MNS) dysfunction hypothesis. We use the cortical underconnectivity framework (Just et al., 2004) to examine the coordination of brain areas that orchestrate the communication between the component skills underlying imitation. A comprehensive account of imitation deficit in autism should take into account the regions that are at the core of the MNS (e.g., IFG and IPL) and related regions that feed into the MNS (e.g., STS, Cerebellum) in their functioning and in their coordination. Our findings suggest that the MNS may be associated with mediating familiarity, attention, self-other matching, and social relevance, which may be vital in characterizing the imitation deficits in autism. Such an analysis may have greater clinical and therapeutic value.