Jain Parul, Conte Mary M, Voss Henning U, Victor Jonathan D, Schiff Nicholas D
Weill Cornell Graduate School of Medical Sciences, New York, NY 10065, USA.
Feil Family Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY 10065, USA.
Brain Commun. 2023 Mar 25;5(2):fcad094. doi: 10.1093/braincomms/fcad094. eCollection 2023.
Assessing cognitive function-especially language processing-in severely brain-injured patients is critical for prognostication, care, and development of communication devices (e.g. brain-computer interfaces). In patients with diminished motor function, language processing has been probed using EEG measures of command-following in motor imagery tasks. While such tests eliminate the need for motor response, they require sustained attention. However, passive listening tasks, with an EEG response measure can reduce both motor and attentional demands. These considerations motivated the development of two assays of low-level language processing-identification of differential phoneme-class responses and tracking of the natural speech envelope. This cross-sectional study looks at a cohort of 26 severely brain-injured patient subjects and 10 healthy controls. Patients' level of function was assessed via the coma recovery scale-revised at the bedside. Patients were also tested for command-following via EEG and/or MRI assays of motor imagery. For the present investigation, EEG was recorded while presenting a 148 s audio clip of . Time-locked EEG responses to phoneme classes were extracted and compared to determine a differential phoneme-class response. Tracking of the natural speech envelope was assessed from the same recordings by cross-correlating the EEG response with the speech envelope. In healthy controls, the dynamics of the two measures were temporally similar but spatially different: a central parieto-occipital component of differential phoneme-class response was absent in the natural speech envelope response. The differential phoneme-class response was present in all patient subjects, including the six classified as vegetative state/unresponsive wakefulness syndrome by behavioural assessment. However, patient subjects with evidence of language processing either by behavioural assessment or motor imagery tests had an early bilateral response in the first 50 ms that was lacking in patient subjects without any evidence of language processing. The natural speech envelope tracking response was also present in all patient subjects and responses in the first 100 ms distinguished patient subjects with evidence of language processing. Specifically, patient subjects with evidence of language processing had a more global response in the first 100 ms whereas those without evidence of language processing had a frontopolar response in that period. In summary, we developed two passive EEG-based methods to probe low-level language processing in severely brain-injured patients. In our cohort, both assays showed a difference between patient subjects with evidence of command-following and those with no evidence of command-following: a more prominent early bilateral response component.
评估重度脑损伤患者的认知功能，尤其是语言处理能力，对于预后判断、护理以及通信设备（如脑机接口）的开发至关重要。对于运动功能减退的患者，已通过运动想象任务中遵循指令的脑电图测量来探究语言处理能力。虽然此类测试无需运动反应，但需要持续注意力。然而，采用脑电图反应测量的被动听力任务可以减少运动和注意力需求。这些考虑因素推动了两种低水平语言处理检测方法的开发——差异音素类别反应的识别和自然语音包络的跟踪。这项横断面研究观察了26名重度脑损伤患者和10名健康对照者。通过床边修订的昏迷恢复量表评估患者的功能水平。还通过运动想象的脑电图和/或磁共振成像检测对患者进行指令遵循测试。在本研究中，在播放一段148秒的音频片段时记录脑电图。提取并比较对音素类别的锁时脑电图反应，以确定差异音素类别反应。通过将脑电图反应与语音包络进行互相关，从相同记录中评估自然语音包络的跟踪情况。在健康对照者中，这两种测量的动态在时间上相似但在空间上不同：自然语音包络反应中不存在差异音素类别反应的中央顶枕成分。差异音素类别反应在所有患者中均存在，包括行为评估分类为植物状态/无反应觉醒综合征的6名患者。然而，通过行为评估或运动想象测试有语言处理证据的患者在前50毫秒有早期双侧反应，而没有任何语言处理证据的患者则没有。自然语音包络跟踪反应在所有患者中也存在，并且前100毫秒的反应区分了有语言处理证据的患者。具体而言，有语言处理证据的患者在前100毫秒有更广泛的反应，而没有语言处理证据的患者在此期间有额极反应。总之，我们开发了两种基于被动脑电图的方法来探究重度脑损伤患者的低水平语言处理能力。在我们的队列中，两种检测方法均显示有指令遵循证据的患者与无指令遵循证据的患者之间存在差异：更突出的早期双侧反应成分。
