脑电研究：ADHD症状儿童对意外声音的反应随年龄段不同

研究做了什么

这项研究关注的是一个很基础的问题：大脑如何自动处理环境里突然出现的声音。按预测编码的框架，大脑会根据刚听到的声音模式建立一个预期模型，当新声音打破这个模式时，会产生一个几百毫秒内的自动电信号，即失匹配负波（mismatch negativity）；如果声音完全陌生，还会出现与不由自主注意相关的后续反应，称为新异反应。另一个关键特征是习惯化：同一声音反复出现时，脑反应通常逐渐减弱，从而把资源留给更重要的目标。

波士顿儿童医院与哈佛医学院的Marija Pranjić、Jirapat Likitlersuang和Anne B. Arnett用脑电（EEG）测量了儿童在被动听音任务中的这些反应。孩子头上戴无害传感器网，看无声视频，同时通过扬声器听一系列声音：多数是重复的标准音，偶尔插入略有不同的音调以触发失匹配负波，也混入鼓点、蟋蟀鸣叫等独特环境声以触发新异反应。任务不需要孩子做任何行为反应，适合年幼儿童。

两个年龄组的不同结果

第一组是115名2.5至5岁幼儿。由于临床很少给这么小的孩子下ADHD诊断，研究者依据综合临床评定分组：64名症状偏高，51名典型发展。结果显示，症状偏高幼儿对意外音调的失匹配负波幅度更大，在控制年龄和认知能力后这一模式仍存在；他们对重复标准音和独特环境声的习惯化也更弱，脑反应没有像典型发展儿童那样随重复试次明显下降。

第二组是71名7至11岁儿童，其中53名有确诊ADHD，18名典型发展，完成同样的听音任务。结果方向相反：ADHD儿童对意外声音的失匹配负波比同龄典型发展儿童更弱；这一年龄组未发现两组在习惯化上的差异，接触新异声音时脑活动随时间下降的程度相近。

能说明什么，不能说明什么

作者把这些年龄差异解释为听觉加工在ADHD中可能随发展而变化：幼儿期对感觉偏差反应偏强，到童年中期则偏弱。这与ADHD涉及早期听觉编码与后续注意选择之间连接异常的理论相符。研究也支持一个更宽的看法：ADHD不只是高级执行功能的问题，基础感觉加工差异可能参与孩子体验和应对周围世界的方式。

但研究设计本身限制了解释力。它是在同一时间点分别测量两个不同年龄组，而非追踪同一批孩子长大，因此无法确定某个孩子的脑反应会如何演变；童年中期的差异究竟代表听觉系统成熟延迟，还是另一条感觉发展路径，目前未知，需要纵向研究回答。此外，结果只表明听觉加工差异与ADHD相关，不能说明这种差异导致ADHD行为。

文章提到，弄清大脑如何过滤声音，未来或许有助于注意障碍的早期识别，也可能为难以屏蔽干扰的儿童设计干预提供线索。这些属于研究者的展望，尚不是已验证的临床应用。

Children with attention-deficit/hyperactivity disorder process unexpected sounds differently than their peers, and these brain responses appear to change as they grow older. A recent study measuring brain waves in two distinct age groups found that children with elevated ADHD symptoms exhibit heightened sensitivity to unexpected tones in early childhood, but diminished sensitivity by middle childhood. These findings were published in the journal Developmental Cognitive Neuroscience.

The human brain constantly monitors the environment for new or unexpected sounds. This ability allows people to adapt to their surroundings and focus on important information while tuning out harmless background noise. In typical development, sensory systems refine their ability to categorize sounds through repeated exposure.

Neuroscientists conceptualize this process through a framework called predictive coding. The brain builds a working model of expected sounds based on recent patterns in the environment. When a new sound breaks that established pattern, the brain generates a specific electrical signal known as mismatch negativity. This rapid response happens in a fraction of a second.

Mismatch negativity operates automatically, without requiring conscious thought. If a completely unique or bizarre sound occurs, the brain generates a secondary electrical signal associated with involuntary attention. This later signal is called a novelty response.

Another important feature of sensory processing is habituation. When a person hears the same sound repeatedly, the brain’s electrical response typically shrinks over time. Habituation helps the brain conserve energy by ignoring irrelevant distractions, freeing up mental resources for goal-directed behavior. Without this ability, a person might feel constantly overwhelmed by everyday background noise.

Researchers Marija Pranjić, Jirapat Likitlersuang, and Anne B. Arnett at Boston Children’s Hospital and Harvard Medical School wanted to understand how these auditory processes operate in children with ADHD. Children with ADHD often struggle with attention regulation and sensory overload. The research team suspected that these everyday challenges might stem from basic differences in how the brain encodes sensory information.

The researchers designed an experiment to test these brain responses across two separate developmental stages. The first part of the study evaluated a group of 115 young children between two and a half and five years old. Participants were excluded if they had a history of seizures, an autism diagnosis, or known genetic syndromes.

Because clinical ADHD diagnoses are rarely given to very young children, the researchers categorized the early childhood group based on comprehensive clinical ratings. Sixty-four children had elevated ADHD symptoms, while 51 children exhibited typical development.

To measure brain activity, the researchers placed a net of harmless sensors on each child’s head to record an electroencephalogram, commonly known as an EEG. The children watched a silent video while listening to a sequence of sounds through speakers. The test required no active behavioral response from the participants. This passive monitoring approach is ideal for studying young children who might struggle with complex instructions.

The sound sequence consisted mostly of a repetitive standard tone. Occasionally, the researchers played a slightly different tone to trigger the brain’s mismatch negativity response. They also mixed in completely unique environmental noises, such as a drum beat or a cricket chirp, to trigger the novelty response.

Pranjić and her colleagues found that young children with elevated ADHD symptoms had a stronger brain response to the unexpected tones. Their mismatch negativity amplitude was larger than that of the children with typical development. This pattern emerged even after the researchers accounted for differences in age and cognitive ability.

The young children with elevated ADHD symptoms also showed differences in habituation. The typically developing children adapted quickly to the repetitive standard tones and the unique environmental noises, showing reduced brain activity over time. In contrast, the brains of the children with elevated ADHD symptoms did not settle down as effectively across the repeated trials.

The researchers then conducted a similar experiment with a separate group of 71 older children. These participants were between seven and eleven years old. In this older group, 53 children had a confirmed ADHD diagnosis, and 18 children were typically developing.

These older participants completed the exact same listening task while the researchers recorded their brain waves. The findings in this older group were quite different from the early childhood group. Children with ADHD in middle childhood exhibited a blunted mismatch negativity response compared to their typically developing peers.

The older children with ADHD showed a weaker brain reaction to unexpected sounds. The researchers did not find evidence of habituation differences between the diagnostic groups in this older cohort. Both the typically developing children and those with ADHD showed similar reductions in brain activity when exposed to the novelty sounds over time.

These age-related differences suggest that sensory processing in ADHD changes over the course of development. In early childhood, the brain might overreact to sensory deviations, while in middle childhood, it might underreact. This shifting pattern aligns with theories that ADHD involves atypical connections between early auditory encoding and later attention selection.

The study design evaluated two distinct age groups at a single point in time, meaning it did not track the same children as they grew older. Because of this cross-sectional approach, researchers cannot say for certain how an individual child’s brain responses evolve. It remains unknown whether the differences seen in middle childhood represent a delayed maturation of the auditory system or an alternative path of sensory development.

Future longitudinal studies, which follow the same participants over many years, are needed to answer these developmental questions. Additionally, the results do not indicate that atypical auditory processing causes ADHD behaviors. The study only demonstrates that altered sensory processing is associated with the condition.

The findings support the idea that ADHD is not exclusively a disorder of higher-order executive functioning. Basic sensory processing differences appear to play an important role in how children experience and interact with the world around them. Understanding exactly how the brain filters sounds could eventually aid in the early detection of attention disorders.

Identifying these biological markers might one day help clinicians design better therapies for children who struggle to tune out distractions. Tracking how sensory adaptation matures across childhood could provide a new window into the developing brain. The study, “Atypical auditory cortical processing in ADHD during early and middle childhood,” was authored by Marija Pranjić, Jirapat Likitlersuang, and Anne B. Arnett.