Mayo Clinic, Department of Neurology, Mayo Systems Electrophysiology Laboratory (MSEL), Rochester MN, USA.
Mayo Clinic, Department of Physiology and Biomedical Engineering, Rochester MN, USA.
Brain. 2017 May 1;140(5):1337-1350. doi: 10.1093/brain/awx043.
Gamma frequency activity (30-150 Hz) is induced in cognitive tasks and is thought to reflect underlying neural processes. Gamma frequency activity can be recorded directly from the human brain using intracranial electrodes implanted in patients undergoing treatment for drug-resistant epilepsy. Previous studies have independently explored narrowband oscillations in the local field potential and broadband power increases. It is not clear, however, which processes contribute to human brain gamma frequency activity, or their dynamics and roles during memory processing. Here a large dataset of intracranial recordings obtained during encoding of words from 101 patients was used to detect, characterize and compare induced gamma frequency activity events. Individual bursts of gamma frequency activity were isolated in the time-frequency domain to determine their spectral features, including peak frequency, amplitude, frequency span, and duration. We found two distinct types of gamma frequency activity events that showed either narrowband or broadband frequency spans revealing characteristic spectral properties. Narrowband events, the predominant type, were induced by word presentations following an initial induction of broadband events, which were temporally separated and selectively correlated with evoked response potentials, suggesting that they reflect different neural activities and play different roles during memory encoding. The two gamma frequency activity types were differentially modulated during encoding of subsequently recalled and forgotten words. In conclusion, we found evidence for two distinct activity types induced in the gamma frequency range during cognitive processing. Separating these two gamma frequency activity components contributes to the current understanding of electrophysiological biomarkers, and may prove useful for emerging neurotechnologies targeting, mapping and modulating distinct neurophysiological processes in normal and epileptogenic brain.
伽马频率活动（30-150Hz）在认知任务中被诱导产生，被认为反映了潜在的神经过程。伽马频率活动可以通过植入正在接受耐药性癫痫治疗的患者的颅内电极直接从人脑记录下来。以前的研究已经独立探索了局部场电位中的窄带振荡和宽带功率增加。然而，尚不清楚哪些过程有助于人类大脑伽马频率活动，或者它们在记忆处理过程中的动态和作用。在这里，使用来自 101 名患者的在单词编码期间获得的颅内记录的大型数据集来检测、描述和比较诱导的伽马频率活动事件。在时频域中分离个体伽马频率活动爆发，以确定它们的频谱特征，包括峰值频率、幅度、频率跨度和持续时间。我们发现了两种不同类型的伽马频率活动事件，它们表现出窄带或宽带频率跨度，揭示了特征性的频谱特性。窄带事件是主要类型，是在宽带事件初始诱导后由单词呈现引起的，它们在时间上是分开的，并且与诱发反应电位选择性相关，这表明它们反映了不同的神经活动，并在记忆编码过程中发挥不同的作用。在随后回忆和遗忘单词的编码过程中，两种伽马频率活动类型的调制方式不同。总之，我们在认知处理过程中伽马频率范围内发现了两种不同活动类型的证据。分离这两种伽马频率活动成分有助于当前对电生理生物标志物的理解，并且可能对针对正常和癫痫大脑中的不同神经生理过程的新兴神经技术的映射和调制有用。
