作者：Caroline Cassels
出處：WebMD醫學新聞
December 2, 2008(芝加哥) — 一個新的腦部影像研究顯示，自閉症系列障礙(autism spectrum disorder，ASD)的小孩在聽覺傳導上會有數秒的延遲，但這可能是影響此類病患語言發展的核心。
前述研究發表於北美放射醫學會第94屆科學研討會暨年會中，使用腦磁圖儀(MEG)的影像研究結果顯示，ASD小孩處理母音聲調比健康小孩慢了幾秒。
主要研究者、賓州兒童醫院的Timothy Roberts博士向Medscape Psychiatry表示，藉由MEG，我們觀察發現，相較於年齡相仿的同儕，自閉症小孩對於一些簡單聲音的處理會有些微明顯的延遲；不過，這只是幾秒之差，但是對於語言會有嚴重的影響。
【與言談理解有關】
他表示，這個延遲反應大約是1/50秒、或稱20毫秒，表面上看來只是個小小的延遲，不過，Roberts博士指出，說話時的音節只持續約四分之一秒、或者250毫秒；他解釋，20毫秒的延遲對於瞭解多音節字彙時會引起相當大的延遲與負擔，所以，自閉症患者比較難跟得上。
MEG一般用來手術前辨識癲癇等病患等的腦部神經活性功能區域；不過，Roberts博士表示，研究者指出，此技術具有提供腦部功能之即時訊息的潛力。
他表示，此觀察以及少數理論派文獻認為，自閉症可能不會有明顯的架構支持，但事實上可能是腦部功能區域的異常連結，因而促成本研究。
他表示，這引起我檢測連接性的一個方法，或者說至少是一種可能的連結失能，將著眼於有關聽覺刺激之神經細胞反應的異常時機。
根據Roberts博士表示，MEG可以擷取腦中的磁性區域，使得可以偵測時間上微妙的延遲，這是其他主要擷取構造性腦部異常的技術，如電腦斷層、核磁共振造影(MRI)或者功能性MRI所無法做到的。
【處理延遲越長 語言缺損越嚴重】
本研究包括64名年紀在6至15歲的研究對象，其中30名有ASD診斷，合併或未合併語言缺損，其他34名小孩是年齡相仿的健康對照組；所有的小孩都接受MEG研究，在一連串的單一音節聲調中檢視他們的聽覺刺激。
Roberts博士表示，我們發現自閉症小孩的聽覺處理有相當程度的延遲，我們無法預期在聽覺處理上這麼早發現問題，實際上是延遲約十分之一秒聽到那個聲音，但是這一旦發生，就是問題。
他指出，這表示有某種的感覺處理問題，和自閉症所見的行為及傳言的觀點不一樣，但這令我驚訝的是，我們可以用相對簡單的聽覺皮質與聽覺處理報告解釋這許多的語言缺損。
此外，研究者發現，延遲的程度與語言缺損程度有關，所以處理延遲越久的小孩，語言缺損越嚴重。
【闡明ASD異質性】
Roberts博士表示，這些發現的價值在於有潛力促進早期診斷與更精確的治療，有助於解開ASD的一些異質性特徵。
我們尋找的或許是個生物標記，可以用來建立自閉症的次類別；每個小孩的延遲程度多少不太一樣，這表示可能需要不同的行為介入。
他表示，舉例來說，ASD特定次類別中，嚴重聽覺處理延遲的小孩，其治療介入可能要更注重在語言治療，而不同於其他延遲較不嚴重的ASD次類別。
目前的自閉症診斷有賴行為與臨床評估，Roberts博士形容為曠時且往往是不確定結果的一些過程，特別是在幼童，語言發展和社會互動技巧上有相當大的變數。
他指出，雖然MEG不太可能取代臨床評估，它最後可能是個可以幫助醫師確認或駁斥ASD診斷的工具。
Roberts博士表示，在歷史上，進行自閉症小孩的研究是困難的，主要是因為他們通常抗拒進行行為測試。
這類病患使用MEG的一個主要好處是，實際上並不需要病童的合作。他表示，這些是腦部對於特定刺激的自動反應，所以我們不用問小孩的反應，我們問的是他們的腦部。
雖然這些結果需要由其他研究者確認，但Roberts博士對於MEG最後將成為ASD或者其他疾病如注意力缺損過動異常之可行的診斷工具感到樂觀。
作者報告沒有相關利益衝突。本研究由國家健康研究中心、Nancy Lurie Marks Family基金會、與Jeffrey and Christina Lurie Family基金會等支持。
RSNA 2008: 北美放射醫學會第94屆科學研討會暨年會：摘要VP11-03。發表於2008年12月1日。
Imaging Study Reveals Explanation for Language Delays in Autism
By Caroline Cassels
Medscape Medical News
December 2, 2008 (Chicago, Illinois) — A new brain imaging study shows children with autism spectrum disorder (ASD) have a very small delay in auditory processing that amounts to fractions of a second but that may be at the heart of the hampered language development that is a common characteristic in this patient population.
Presented here at the 94th Scientific Assembly and Annual Meeting of the Radiological Society of North America, results of an imaging study using magnetoencephalography (MEG) show that children with ASD process vowel sounds and tones a fraction of a second more slowly than healthy controls.
"Using MEG, we observed that there is a small but robust delay in the evoked response to simple sound processing in children with autism, compared with their age-matched peers. Although we are only talking about fractions of a second, these can have a catastrophic impact on spoken language," principal investigator Timothy Roberts, PhD, from Children's Hospital of Philadelphia, in Pennsylvania, told Medscape Psychiatry.
Playing Catch-Up
This delayed response, he said, is approximately 1/50th of a second, or 20 ms. On the surface this small delay may seem of little consequence. However, Dr. Roberts noted that a spoken syllable only lasts a quarter of a second, or 250 ms. A 20-ms delay in detecting a syllable in a multisyllable word, he explained, leads to a "cascade of delay" and overload so that, in effect, an individual with autism is never able to catch up.
MEG is routinely used for presurgical mapping to identify areas of functional brain activity in patients with neurological conditions such as epilepsy. However, said Dr. Roberts, the investigators noticed the technology had the potential to offer insights into the timing of brain function.
This observation, he said, coupled with an awareness of a small body of theoretical literature indicating that autism may not have obvious structural underpinnings but may in fact be consequent to abnormal connectivity of brain functional areas led to the current study.
"It occurred to me that 1 way of testing connectivity, or at least a possible dysfunction of connectivity, would to look at the abnormal timing of neuro–nerve cell activity in response to [auditory] stimuli," he said.
According to Dr. Roberts, the ability of MEG to pick up magnetic fields in the brain makes it ideally suited to detect subtle delays in timing that would not be visible with other technologies, including computed tomography, magnetic resonance imaging (MRI), or functional MRI, which primarily pick up structural brain abnormalities.
Longer Processing Delays, More Severe Language Impairment
The study included 64 subjects aged 6 to 15 years. Of these, 30 had a diagnosis of ASD, with or without concomitant language impairment. The remaining 34 children were healthy, age-matched controls.
All children underwent MEG studies in which they were presented with auditory stimuli in the form of single vowel sounds or tones in rapid succession.
"We found a very robust delay in auditory processing right across the board in children with autism. We didn't expect to see a problem so early in the auditory process, literally a tenth of a second after hearing a sound, and yet that is when it showed up," said Dr. Roberts.
"This suggests there is some sort of sensory processing problem, which is not inconsistent with behavioral and anecdotal views on autism, but I think it is surprising we can account for such a lot of the language impairment with relatively straightforward auditory cortex and auditory processing observations," he added.
In addition, the researchers found the degree of delay was well correlated with the degree of language impairment, so that children with longer processing delays had more severe language impairment.
Unraveling ASD Heterogeneity
The value of these findings, said Dr. Roberts, lies in their potential to facilitate earlier diagnosis and more targeted treatment and to help unravel some of the heterogeneity that characterizes ASD.
"What we are seeing here perhaps is a biomarker that might be used to create subpopulations of autism. Some children may display more or less of these delays, which might warrant different behavioral interventions."
For instance, he said, a child in a particular subpopulation of ASD with severe auditory processing delays may have a treatment intervention that has a greater focus on speech therapy vs a child in another ASD subpopulation with less severe auditory processing difficulties.
Current diagnosis of autism relies on behavioral and clinical assessment, which Dr. Roberts described as a time-consuming and frequently uncertain process, particularly in very young children, where there can be significant variability in the development of language and social skills.
While MEG is unlikely to replace clinical evaluation, it could turn out to be a valuable tool that would help clinicians confirm or refute a diagnosis of ASD, he added.
Historically, said Dr. Roberts, conducting outcomes research in children with autism has been difficult, mainly because they are often resistant to performing behavioral tests.
One of the major advantages of using MEG in this patient group is the fact that it does not require the cooperation of the child. "These are automatic responses of the brain to particular stimuli, so we don't ask the child to respond, we ask the child's brain," he said.
While these results need to be confirmed by other investigators, Dr. Roberts is optimistic MEG will eventually turn out to be a viable diagnostic tool for ASD and possibly other conditions, including attention deficit hyperactivity disorder.
The authors report no relevant conflicts of interest. The study was supported by the National Institutes of Health, the Nancy Lurie Marks Family Foundation, and the Jeffrey and Christina Lurie Family Foundation.
RSNA 2008: 94th Scientific Assembly and Annual Meeting of the Radiological Society of North America: Abstract VP11-03. Presented December 1, 2008.
[ 本帖最後由 goodcat1111 於 2008-12-15 13:24 編輯 ] |
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