在日常生活中,可预测的感官刺激通常不会提供生态信息。相比之下,新的或意想不到的刺激表明环境在生态学上发生了显着变化。这个想法构成了预测编码假设的基础:有效的感觉编码最大限度地减少了与可预测背景相关的神经活动,并强调了对环境变化的检测。在现实生活中,大脑必须解决在不同时间尺度上发生的多个意外感官事件。局部/全局偏差实验范式检查多个时间尺度上的听觉预测编码。对于短期的新颖性[数百毫秒;局部偏差 (LD)],相同声音序列 (/xxxxx/) 散布在包含偏差 (/xxxxy/) 的序列中。长期新颖性[几秒钟;全局偏差 (GD)] 是使用 (a) 频繁的 /xxxxx/ 和不频繁的 /xxxxy/ 序列,或 (b) 频繁的 /xxxxy/ 和不频繁的 /xxxxx/ 序列创建的。在场景 (a) 中,同时存在 LD 和 GD 效应(LDGD,“双重惊喜”)。在 (b) 中,全局偏差是局部标准,即相同声音序列 (LSGD)。反映 LD 和 GD 的皮层反应起源于不同的大脑区域,具有不同的时间过程,并且对全身麻醉的敏感性不同。LD 和 GD 的基础神经过程已被证明是相互作用的,反映了重叠网络有助于检测新的听觉刺激。本研究使用神经外科患者的颅内脑电图检查了这些相互作用。受试者在异丙酚麻醉诱导之前和期间执行 GD 目标检测任务。录音是从听觉皮层、周围的听觉相关皮层和前额叶皮层在清醒、镇静和无反应状态下进行的。高伽马活动用于测量局部到全局新奇交互的神经基础。与 LSGD 相比,积极互动被定义为对双重惊喜 LDGD 条件的更大反应。负面互动被定义为对 LDGD 的较弱反应。积极互动比消极互动更频繁,主要存在于听觉皮层。负相互作用通常发生在前额叶皮层,对全身麻醉更敏感。颞顶叶听觉相关区域表现出两种类型的相互作用。
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Arousal State-Dependence of Interactions Between Short- and Long-Term Auditory Novelty Responses in Human Subjects
In everyday life, predictable sensory stimuli are generally not ecologically informative. By contrast, novel or unexpected stimuli signal ecologically salient changes in the environment. This idea forms the basis of the predictive coding hypothesis: efficient sensory encoding minimizes neural activity associated with predictable backgrounds and emphasizes detection of changes in the environment. In real life, the brain must resolve multiple unexpected sensory events occurring over different time scales. The local/global deviant experimental paradigm examines auditory predictive coding over multiple time scales. For short-term novelty [hundreds of milliseconds; local deviance (LD)], sequences of identical sounds (/xxxxx/) are interspersed with sequences that contain deviants (/xxxxy/). Long-term novelty [several seconds; global deviance (GD)] is created using either (a) frequent /xxxxx/ and infrequent /xxxxy/ sequences, or (b) frequent /xxxxy/ and infrequent /xxxxx/ sequences. In scenario (a), there is both an LD and a GD effect (LDGD, “double surprise”). In (b), the global deviant is a local standard, i.e., sequence of identical sounds (LSGD). Cortical responses reflecting LD and GD originate in different brain areas, have a different time course, and are differentially sensitive to general anesthesia. Neural processes underlying LD and GD have been shown to interact, reflecting overlapping networks subserving the detection of novel auditory stimuli. This study examined these interactions using intracranial electroencephalography in neurosurgical patients. Subjects performed a GD target detection task before and during induction of anesthesia with propofol. Recordings were made from the auditory cortex, surrounding auditory-related and prefrontal cortex in awake, sedated, and unresponsive states. High gamma activity was used to measure the neural basis of local-by-global novelty interactions. Positive interaction was defined as a greater response to the double surprise LDGD condition compared to LSGD. Negative interaction was defined as a weaker response to LDGD. Positive interaction was more frequent than negative interaction and was primarily found in auditory cortex. Negative interaction typically occurred in prefrontal cortex and was more sensitive to general anesthesia. Temporo-parietal auditory-related areas exhibited both types of interaction. These interactions may have relevance in a clinical setting as biomarkers of conscious perception in the assessment of depth of anesthesia and disorders of consciousness.