Cortical Activation During Sentence Comprehension Using Functional MRI
Introduction
This study examines the brain activation during sentence comprehension using functional MRI. Researchers conducting this experiment are studying how the activation of high functioning autistic individuals compared to the control participants differ in terms of activation. For this research, we are analyzing the comparisons of the activations in different areas of the brain with connection to some of the key languages. In addition to this, researchers in this experiment will focus on the synchronization of activations in the different (cortical) areas. Based on previous studies focusing on neuroimaging, it is shown that in normal individuals, they have a number of cortical areas that become activated during sentence comprehension. These studies have then lead researchers to investigate in language processing in autism.
One theory that was discussed relating to the study, is neurologists Luria (1980) and Mesulam (1990) wanted an explanation on why patients with focal lesions usually display non-focal cognitive deficits. They theorized that the anatomical pathways between potentially collaborating cortical areas provide the communication infrastructure for the proposed collaborative nature of the processing. In this study, this theory may help these researchers with their study on autism because it leads them to examine the cortical activation at a system level instead of a single area (level).
Another theory by Horwtiz is used to demonstrate the relationship between the correlations with frontal and parietal cortices by using the PET scan. In this theory, Hortwitz uses the PET scan to demonstrate the reduced intra and interhemispheric correlations with the different cortices. This study supports the theory that whether the activation levels of a pair of regions of interest were correlated with each other using the PET to measure the outcomes.
Method
For the study, seventeen high functioning autistic and 17 healthy normal participants were used. The participants all had a full scale and verbal IQ of 80 or above. The autistic participants had to meet all 3 criteria in order to participate. Ones who associated disorders were excluded which was based on their examination. (Controlled) participants were screened with questionnaires, interviews, observations during screening tests and were evaluated throughout these procedures. Materials that were a comprehension task which was to read an active or passive sentence and respond to a probe which they had to identify the agent or recipient of the action by pressing buttons that are correlated to the answers. In the procedure, each testing session consisted of a SPGR (structural spoiled gradient recalled) scan. A GEmedical systems 3. 0 scanner and functional echo planar scans and pulse were also used and imaged. This tested an equal amount of participants strength in each field. In controversy, a small portion of the participants from the autism and control groups without clear left lateralization in this task were excluded from further analysis.
From the results found, researchers used SPM99 to analyze the data. They used statistical analysis on the group and individual data by using the Gaussian random field theory as well as the general linear model. The functional connectivity of the participants was calculated as a correlation between the average time course of all the activated voxels in each member of a pair. For the functional connectivity to be measurable, 3 voxels at minimum were required in each member of the ROI. Participants (control) who were shown to have extremely high functional activity were considered outliers and were then excluded from the functional connectivity analysis. 35 ROIs were defined for each participant in a sentence using a conventional cortical parcellation scheme. In reference to the methods, I believe the internal validity is high, it is very strong in following the experiment. The researchers conducting the experiment are shown to be avoiding confounding which refers to avoiding having more than one possible independent variable. In this study, we see that we have two groups, the control group (which is the independent variable) and the autism group to compare the results and findings of the experiment. They are comparing data and analysis with the different control groups and autistic groups which can lead to a high internal validity. As for the design of the experiment and study, I believe it is pretty solid. So far, I do not see any issues with the methodology except a concern in the exclusions they are proceeding with during the experiments which can alter or affect the final results. These exclusions could further explain some defects in the results or explain the outcomes of the findings which I think is important in terms of the study.
The results found
The results were shown a difference between the two groups in the distribution of activation in Broca’s area and Wernicke’s area. The autistic participants were shown to have less activation in the LIFG than the control group, but more activation in the LSTG than the control group. In the functional connectivity, the pairs between ROIs were lower for the autistic participants than for the control group. When the two groups were compared in each ROIs pair separately, all of the 10 reliable differences showed a lower functional connectivity in the autistic group. This group participants had a lower mean connectivity of 0. 58 compared to the control group (0. 61). Nevertheless, the two groups had a similar ordering (r=0. 98) of functional connectivities of the different ROI pairs but the levels of synchronization were lower in the autistic group. In the behavioral performance area, the results suggested that the autistic group performed the task faster and less accurately with a mean time reaction of 2456 and 2803. Error rates for the autistic group were 8 and 13% while the control group rates were 5 and 7%, showing a slight increase in the autistic group. The data indicates that the results of the autistic group are less proficient at semantically assimilating words in a sentence. This then results into more errors for the more complex passive sentences.
Discussion
Conclusions that were drawn from the results is that based on the results, the findings of the experiment showed that compared with the controls, the autistic participants engage in more extensive processing of the meanings of the individual words that comprise a sentence, which is more consistent with their unusual strength in processing words. The results suggest that, compared to the control group, the high functioning autistic individuals engage less in the aspect of sentence aspects of sentence processing while also requiring more coordination and a poorer integration of information at higher levels of processing and require more coordination. These findings and results do seem reasonable because they are consistent with the semantic, syntactic and working memory processes.
In accordance of the results of the autistic groups lower activation, higher functioning autistic participants are impaired in their ability to process complex sentences. The underconnectivity theory predicted that any function part of the (psychological or neurological) that is dependent on the coordination of the brain region is prone for disruption. This theory supports the authors interpretations based on his proposal that of how autism is a cognitive and neurobiological disorder that is caused by under functioning integrative circuitry which results in a deficit of integration of information at the neural and cognitive levels.
These results and findings apply to the real world because as mentioned, social interactions place large demands on information integration. Abnormalities or changes can arise in integrating the perceptual and affective processing of social stimuli. The theory of mind that occurs in autism could itself be the outcome of a deficit in integrating social and cognitive processing. Another example is how the interconnectivity could explain the difficulty in novel cognitive tasks. In such situation, the inter-regional coordination is very critical. The poorer connectivity in autism impairs the dynamic ability of supporting the brain regions to dynamically configure themselves into networks.
