Critical Analysis Of The Study On The Role Of The Anterior Temporal Lobe In Sentence Processing
Background
According to the National Aphasia Association (NAA) Primary Progressive Aphasia (PPA) can be defined as “a neurological syndrome in which language capabilities become slowly and progressively impaired. ” (aphasia. org) PPA differs from other forms of aphasia because it is caused by “neurodegenerative diseases, such as Alzheimer’s disease or Frontotemporal Lobar Degeneration. PPA results from deterioration of brain tissue important for speech and language. There are three types of PPA semantic, logopenic, and nonfluent a-grammatic. ” (aphasia. org) From these three types of PPA research conducted by the Massachusetts Institute of Technology (MIT) published in the Journal of Cognitive Neuroscience focuses on the semantic variant of PPA.
In semantic variant Primary Progressive Aphasia (svPPA) a patient will show “impaired performance on measures that depend on intact semantics. ” (NIH) Patients with svPPA “have difficulty with picture and object naming, single word comprehension, category naming fluency, and knowledge of the uses and features of objects. ” (NIH). As mentioned in the American Speech and Language Hearing Association (ASHA) in svPPA “speech is articulate, and syntax is intact. ” (ASHA Journal) “As time goes on, people with svPPA begin to use more general names for specific things.
For example, they might say “animal” instead of “dog”. ” (memory. ucsf. edu) The area with greatest atrophy in svPPA is the anterior and inferior temporal cortex. (PPA Argye E. Hillis) It is also associated with frontotemporal lobar degeneration (FTLD). This information is provided to thoroughly understand the study provided in MIT’s Journal of Cognitive Neuroscience. The study performed encompasses the following “What role does the anterior Temporal Lobe play in sentence-level processing? Neural correlates of Syntactic Processing in Semantic Variant Primary Progressive Aphasia.
Study Aims/Hypotheses
The study conducted by MIT is aimed to discuss the role of the Anterior Temporal Lobe (ATL) in sentence-level processing with syntactic structure building and combinatorial semantic processing. Both neuroimaging and neuropsychological studies have shown that the ATL plays a role in these functions. However, this article highlights a challenge to this view through the studying of neural correlates in patients with semantic PPA where the patient has difficulty with semantics, yet their syntax is spared. These findings caused two questions to arise in the study. First, they examined which parts of the brain are usually involved in “syntactic processing and are damaged in semantic PPA by comparing activations for syntactic processing in age-matched controls with patterns of atrophy in semantic PPA”. (MIT article) The second question they aimed to answer was whether “spared syntactic processing depends on preserved functionality of intact regions, preserved functionality of atrophic regions, or compensatory functional reorganization. ” (MIT article) The hypotheses of this study deduced that “if the ATL is critical for syntactic processing, which is largely spared in semantic PPA, then we would expect that syntactic processing in semantic PPA would depend on preserved functionality in the ATL despite atrophy and/or functional reorganization such that relatively intact regions compensate for the damaged ATL. ” (MIT article).
Summary of Study
The design of this study consisted of scanning participants with fMRI while they completed an auditory sentence-to-picture matching task. At the beginning of each trial the participant was presented with two pictures. The first picture showed a target and the other showed a foil. The pictures were placed both on the left and right of the screen. After a second passed, a sentence was read to the participants auditorily that coincided with one of the pictures previously shown. The participants were able to select the picture that matched by pressing a button with their right hand. In the experimental design there were seven conditions which differed both in length and in syntactic processing required. These conditions were Short lexical, Short Active, Short Passive, Long Lexical, Long Easy, Long Medium, and Long Hard. “Within each length category (short or long), all conditions were matched for length, for lexical content, and for the point at which the sentence disambiguated between the target and foil pictures. ” (MIT journal) Since patients with semantic PPA suffer from severe lexical deficits no “scrambled” condition was included, and the sentences provided were made with only two nouns (boy, girl), one of seven high frequency verbs (push, pull, kiss, kick, chase, wash, hug) and for longer sentences one of three adjectives (red, blue, green). (MIT Journal). Before beginning the task, the participants were trained and scanned on a Siemens 3-T trio scanner. The auditory stimuli provided in the task were delivered by headphones, pictures were provided by a screen viewed through a mirror, and the buttons pressed during the selection process recorded the total duration of each test which was 15 minutes and 40 seconds. (MIT journal) Overall, “participants performed a sentence comprehension task that emphasized syntactic processing and minimized lexical semantic demands. ” (MIT Journal).
Methods/Participants
The methods used in this study required finding and completing functional imaging data in participants that had semantic PPA and age-matched controlled participants. Over a period of 4 years, the researchers were able to acquire 20 patients with svPPA and 24 age-matched control participants. (MIT) Patients were recruited through the memory and aging center at the University of California San Francisco (UCSF). Both patients and controls received thorough evaluation of: neurological history, and examination, neuropsychological testing, and neuro imaging and gave written consent. A variety of factors were considered when selecting patients and controls for this study. They chose their patients with PPA based on the most current guidelines for diagnosis. Such criteria required the patient to show “progressive deterioration of speech and/or language functions and that deficits be largely restricted to speech and/or language for at least 2 years. ”(MIT JOURNAL)
In order for the patient to be diagnosed with semantic variant PPA two principal features had to be present “impaired confrontation naming and impaired single word comprehension. At least three of the four following features were also required: impaired object knowledge, surface dyslexia or dysgraphia, spared repetition and spared speech production. ” (MIT journal) Additionally, patients needed to be fluent in English and pass a Mini-Mental State Examination score of at least 15. When choosing participants, the study also took into consideration demographic, clinical, language production, language comprehension, visuospatial function, visual memory, verbal memory, and executive function factors. Overall, they found “no significant differences in age, sex, handedness, or education. As expected, semantic PPA patients had significant deficits on all measures related to lexical semantic function, including confrontation, naming and auditory word recognition. ” (MIT ARTICLE)
Results
The study provided by Wilson, aimed to answer two questions: “Which regions normally involved in syntactic processing are damaged in semantic PPA? and does spared syntactic processing in semantic PPA depend on preserved functionality of intact regions, preserved functionality of atrophic regions, or compensatory functional reorganization? ”(MIT JOURNAL) The findings for the first question this study aimed to answer showed that in controls left inferior front and left posterior temporal regions were used for syntactic processing however the anterior temporal regions were not used. Atrophy in the anterior temporal lobe of semantic variant PPA patients was noted as most severe but also affected the posterior temporal regions used for syntactic processing. For the second question similar results were found for both participants with svPPA and controls. Whole-brain analyses showed there was no significant difference in the areas of the brain used for syntactic processing. According to the text the findings show “spared syntactic processing in semantic PPA depends on preserved functionality of moderately atrophic regions (posterior temporal cortex and anterior insula). Although there were some significant differences in functional activity between semantic PPA patients and controls, there were no patterns suggestive of functional reorganization, that is, no novel regions were modulated by syntactic processing in semantic” PPA. (MIT article)
Opinion
The study was very interesting and specific to the field of Speech-Language Pathology and understanding the different processes responsible for syntactic processing in semantic variant PPA. The article clearly expressed the main points of research by stating the view being challenged, why they were challenging this view, their hypotheses, and the evidence gathered to prove their argument. I believe the article provided appropriate information to uphold their argument and presented solid results of their findings. Wilson provides appropriate background in the beginning of the article to assist the reader in understanding the meaning of aphasia and the type of aphasia that would be discussed svPPA. The methods of the experiment were satisfactory as they assured proper diagnosis of svPPA based on recent guidelines and required a list of characteristics the patient must show to be diagnosed. This is very important to support their findings of the role of the ATL in syntactic processing for patients with svPPA. The study also assured proper criteria for their controls by requiring them to pass a mental state examination as well as no significant differences in demographic, clinical, and neuropsychological characteristics for all participants. The experimental design was adequate to test their hypotheses. They used proper scans as the participants performed the auditory sentence-to-picture matching task and provided a wide range of conditions and appropriate tasks with minimum lexical demands to guarantee accurate results from patients with svPPA. The study’s result, and conclusions are consistent with the data collected and the scans presented.
Possible Limitations
Possible limitations of this article include that there are many other studies that have been done that show the role of the ATL in syntactic processing. These other studies show the opposing argument discussing the activation of the ATL in syntactic processing. This study’s main argument for the role of the ATL in syntactic processing is based on the argument that the task they presented to the participant of sentence-to-picture matching shows new findings that in fact prove the role of the ATL in sentence level processing is unlikely related to syntactic structure-building. Since there are limited studies that argue the view that the ATL does not play a significant role in syntactic processing there is a limitation in their argument because of the amount of evidence presented against this theory.
According to another study by Rogalsky and Hickok, “previous research has implicated the anterior temporal cortex in processing speech containing syntactic structure. Similarly, in the present study, we found that bilateral ATL regions demonstrated an increased BOLD response while listening to sentences compared with noun lists. ”( Rogalsky and Hickok,) In this study PPA is used to challenge the idea that the ATL plays a role in syntactic processing because in patients with svPPA the ATL has severe atrophy yet syntax is spared. A limitation arises when using svPPA as a support because they could have included other challenges besides svPPA to the idea that the ATL is involved in syntactic aspects of sentence processing. Additionally, Brennan in the article Syntactic structure building in the anterior temporal lobe during natural story listening discusses an opposing view that “our primary finding is that a measure of syntactic structure building is correlated with activity in the left anterior temporal lobe supporting the view that the left anterior temporal cortex contributes to the processing of syntactic composition. ”)Brennan
Future Research
Studying the neural correlates of syntactic processing in semantic progressive aphasia provides new insight to the way processes work in the brain of patients with aphasia and offers further understanding of the effects of aphasia. This article contributes to future research examining the neural basis of sentence processing and can aid in research specifically for patients with semantic progressive aphasia. There is no cure for svPPA and are “fighting against a condition in which they will continue to lose their ability to speak, write, and/or understand what they hear. However, individuals with PPA may benefit during their illness by acquiring new communication strategies from Speech-Language Pathologists. ” This article can provide insight into future research on how to help patients with PPA gain new communication strategies by studying the language regions of the brain and what areas are specifically affected professionls will be better prepared to treat these individuals suffering from svPPA. Application
Clinical work
As a Speech and Language Pathologist (SLP), this study is an excellent resource to broaden knowledge on the regions of the brain involved in syntactic processing. SLP’s are experts in communication who work with a wide population from babies to adults to treat communication and swallowing problems. Among their wide scope of practice, they treat language disorders in adults which can translate to an aphasia in some cases. Patients with Primary Progressive Aphasia will be treated by a team of professionals to help them adjust their lifestyle to the disability they are dealing with. Specifically, a Speech and Language Pathologist working in a skilled nursing facility (SNF) may work daily with a person who has PPA. The information provided in this article would assist an SLP working in a SNF setting by providing insight into how syntactic processing functions in patients with semantic PPA. SLP’s must become very familiar with the anatomy and physiology of the brain to treat different speech and language disorders. The article provides an overview of the different brain scans used to understand the language regions of the brain and how they are used to understand the disorders a patient may be displaying in Speech and Language.
