人腦聽覺區於相同與橫跨皮質深度之特徵依賴性固有功能性連結研究

Abstract

在大腦聽覺區對於聲音訊息的處理過程中，腦神經元對於不同頻率訊息的偏好與調頻的頻寬為兩項重要特徵。但聲音訊息不僅需要拆開於不同的頻帶進行處理，更需要在最後將訊息整合以獲得有意義的輸出。由於腦神經元已知在橫跨腦皮質層的方向有不同的連結型態，探討橫跨大腦聽覺區皮質深度的功能性連結將有助於理解聲音訊息的整合處理。在本篇論文中，我們使用功能性磁共振影像，搭配自製的磁共振影像接收線圈陣列與基於表面的腦皮質層分析，來研究人腦聽覺區於相同與橫跨皮質深度的頻率偏好、調頻頻寬依賴性的固有功能性連結。我們發現特徵依賴性的固有功能性連結存在於聽覺區核心與非核心區域的所有皮質深度。相同皮質深度的頻率偏好依賴性固有功能性連結，在聽覺區核心區域的深層較中間層與表層皮質擁有更高的選擇性。相同皮質深度的頻率偏好、調頻頻寬依賴性固有功能性連結，在聽覺區深層皮質的核心區域較非核心區域擁有更高的選擇性。進一步地分析橫跨皮質深度的固有功能性連結，我們發現類似的結果，且橫跨皮質深度的特徵依賴性固有功能性連結擁有之選擇性，會隨著兩個皮質深度的距離增加而下降。總結來說，本篇論文提供了證據說明人腦聽覺區擁有皮質深度專一的特徵依賴性固有功能性連結。

Frequency preference and spectral tuning are two cardinal features of information processing in the auditory cortex. However, sounds should not only be processed in separate frequency bands because information needs to be integrated to be meaningful. One way to better understand the integration of acoustic information is to examine the functional connectivity across cortical depths, as neurons are already connected differently across laminar layers. Using a tailored receiver array and surface-based cortical depth analysis, we revealed the frequency–preference as well as tuning–width dependent intrinsic functional connectivity (iFC) within and across cortical depths in the human auditory cortex using functional magnetic resonance imaging (fMRI). We demonstrated feature-dependent iFC in both core and noncore regions at all cortical depths. The selectivity of within-depth frequency–preference dependent iFC was higher at deeper depths than at intermediate and superficial depths in the core region. Both the selectivity of within-depth frequency–preference and tuning–width dependent iFC were stronger in the core than in the noncore region at deep cortical depths. Further analysis of cross-depth iFC shows similar results, while the selectivity of cross-depth feature-dependent iFC decreased when two cortical depths were farther away from each other. Taken together, our findings provide evidence for a cortical depth-specific feature-dependent functional connectivity in the human auditory cortex.