Ramos Tiago, Ramos Júlia, Pais-Vieira Carla, Pais-Vieira Miguel
iBiMED-Institute of Biomedicine, Department of Medical Sciences, University of Aveiro, 3810-193 Aveiro, Portugal.
Faculdade de Ciências da Saúde e Enfermagem, Centro de Investigação Interdisciplinar em Saúde (CIIS), Universidade Católica Portuguesa, 4169-005 Porto, Portugal.
Brain Sci. 2024 Sep 11;14(9):915. doi: 10.3390/brainsci14090915.
The neural basis of tactile processing in humans has been extensively studied; however, the neurophysiological basis of human width discrimination remains relatively unexplored. In particular, the changes that occur in neural networks underlying active tactile width discrimination learning have yet to be described. Here, it is hypothesized that subjects learning to perform the active version of the width discrimination task would present changes in behavioral data and in the neurophysiological activity, specifically in networks of electrodes relevant for tactile and motor processing. The specific hypotheses tested here were that the performance and response latency of subjects would change between the first and the second blocks; the power of the different frequency bands would change between the first and the second blocks; electrode F4 would encode task performance and response latency through changes in the power of the delta, theta, alpha, beta, and low-gamma frequency bands; the relative power in the alpha and beta frequency bands in electrodes C3 and C4 (Interhemispheric Spectral Difference-ISD) would change because of learning between the first and the second blocks. To test this hypothesis, we recorded and analyzed electroencephalographic (EEG) activity while subjects performed a session where they were tested twice (i.e., two different blocks) in an active tactile width discrimination task using their right index finger. Subjects (n = 18) presented high performances (high discrimination accuracy) already in their first block, and therefore no significant improvements were found in the second block. Meanwhile, a reduction in response latency was observed between the two blocks. EEG recordings revealed an increase in power for the low-gamma frequency band (30-45 Hz) for electrodes F3 and C3 from the first to the second block. This change was correlated with neither performance nor latency. Analysis of the neural activity in electrode F4 revealed that the beta frequency band encoded the subjects' performance. Meanwhile, the delta frequency band in the same electrode revealed a complex pattern where blocks appeared clustered in two different patterns: an Upper Pattern (UP), where power and latency were highly correlated (Rho = 0.950), and a sparser and more uncorrelated Lower Pattern (LP). Blocks belonging to the UP or LP patterns did not differ in performance and were not specific to the first or the second block. However, blocks belonging to the LP presented an increase in response latency, increased variability in performance, and an increased ISD in alpha and beta frequency bands for the pair of electrodes C3-C4, suggesting that the LP may reflect a state related to increased cognitive load or task difficulty. These results suggest that changes in performance and latency in an active tactile width discrimination task are encoded in the delta, alpha, beta, and low-gamma frequency bands in a fronto-central network. The main contribution of this study is therefore related to the description of neural dynamics in frontal and central networks involved in the learning process of active tactile width discrimination.
人类触觉处理的神经基础已得到广泛研究;然而,人类宽度辨别能力的神经生理学基础仍相对未被探索。特别是,主动触觉宽度辨别学习背后神经网络中发生的变化尚未得到描述。在此,我们假设学习执行宽度辨别任务主动版本的受试者在行为数据和神经生理活动方面会出现变化,特别是在与触觉和运动处理相关的电极网络中。这里测试的具体假设是,受试者在第一个和第二个组块之间的表现和反应潜伏期会发生变化;不同频段的功率在第一个和第二个组块之间会发生变化;电极F4将通过δ、θ、α、β和低γ频段功率的变化来编码任务表现和反应潜伏期;电极C3和C4中α和β频段的相对功率(半球间频谱差异-ISD)会因第一个和第二个组块之间的学习而发生变化。为了验证这一假设,我们在受试者使用右手食指执行主动触觉宽度辨别任务并接受两次测试(即两个不同组块)的过程中记录并分析了脑电图(EEG)活动。受试者(n = 18)在第一个组块中就已经表现出较高的表现(高辨别准确率),因此在第二个组块中未发现显著改善。同时,观察到两个组块之间反应潜伏期有所缩短。EEG记录显示,从第一个组块到第二个组块,电极F3和C3的低γ频段(30 - 45 Hz)功率增加。这种变化与表现和潜伏期均无关联。对电极F4神经活动的分析表明,β频段编码了受试者的表现。同时,同一电极中的δ频段呈现出一种复杂模式,组块以两种不同模式聚类:一种是上部模式(UP),其中功率和潜伏期高度相关(Rho = 0.950),另一种是更稀疏且相关性更低的下部模式(LP)。属于UP或LP模式的组块在表现上没有差异,也不特定于第一个或第二个组块。然而,属于LP的组块反应潜伏期增加、表现变异性增加,并且电极对C3 - C4在α和β频段的ISD增加,这表明LP可能反映了一种与认知负荷增加或任务难度增加相关的状态。这些结果表明,主动触觉宽度辨别任务中表现和潜伏期的变化在额中央网络的δ、α、β和低γ频段中进行编码。因此,本研究的主要贡献在于描述了参与主动触觉宽度辨别学习过程的额叶和中央网络中的神经动力学。