Department of Biology, Freie Universität Berlin, Berlin, Germany; Institute of Mental Health Research, University of Ottawa, Ontario, Canada.
Hum Brain Mapp. 2014 Jan;35(1):173-84. doi: 10.1002/hbm.22166. Epub 2012 Sep 21.
Awareness is an essential feature of the human mind that can be directed internally, that is, toward our self, or externally, that is, toward the environment. The combination of internal and external information is crucial to constitute our sense of self. Although the underlying neuronal networks, the so-called intrinsic and extrinsic systems, have been well-defined, the associated biochemical mechanisms still remain unclear. We used a well-established functional magnetic resonance imaging (fMRI) paradigm for internal (heartbeat counting) and external (tone counting) awareness and combined this technique with [(18)F]FMZ-PET imaging in the same healthy subjects. Focusing on cortical midline regions, the results showed that both stimuli types induce negative BOLD responses in the mPFC and the precuneus. Carefully controlling for structured noise in fMRI data, these results were also confirmed in an independent data sample using the same paradigm. Moreover, the degree of the GABAA receptor binding potential within these regions was correlated with the neuronal activity changes associated with external, rather than internal awareness when compared to fixation. These data support evidence that the inhibitory neurotransmitter GABA is an influencing factor in the differential processing of internally and externally guided awareness. This in turn has implications for our understanding of the biochemical mechanisms underlying awareness in general and its potential impact on psychiatric disorders.
意识是人类思维的一个基本特征，可以指向内部，即自我，也可以指向外部，即环境。内部和外部信息的结合对于构成我们的自我意识至关重要。尽管已经明确了潜在的神经元网络，即所谓的内在系统和外在系统，但相关的生化机制仍不清楚。我们使用了一种成熟的功能性磁共振成像（fMRI）范式来进行内部（心跳计数）和外部（音调计数）意识，并将这种技术与同一组健康受试者的 [(18)F]FMZ-PET 成像相结合。关注皮质中线区域，结果表明这两种刺激类型都会在 mPFC 和楔前叶引起负的 BOLD 反应。通过仔细控制 fMRI 数据中的结构噪声，在使用相同范式的独立数据样本中也证实了这些结果。此外，与注视相比，当与外部意识而不是内部意识相关联时，这些区域内 GABA 受体结合潜力的程度与神经元活动变化相关。这些数据支持了抑制性神经递质 GABA 是对内源性和外源性导向意识进行差异处理的影响因素的证据。这反过来又对我们理解意识的生化机制及其对精神疾病的潜在影响具有重要意义。
