Background: Individuals with late-life depression can be divided into two categories, those with early and late-onset depression (EOD and LOD, respectively). It has been reported that LOD has more accentuated subcortical vascular lesions and frontal lobe dysfunction (hypofrontality). The aim of the present study was to examine whether LOD exhibits more prominent hypofrontality than EOD during performance of the word fluency task (WFT) under multichannel near-infrared spectroscopy (NIRS), a newly developed non-invasive functional neuroimaging technique.
Methods: Eleven patients with EOD, 12 patients with LOD, and 13 healthy controls participated in the study. Clinical symptoms of depression were equivalent in the EOD and LOD groups. Brain magnetic resonance imaging demonstrated more robust subcortical vascular changes in LOD than EOD. The NIRS images were obtained using an ETG-4000, 52-channel NIRS system (Hitachi Medical, Tokyo, Japan). Mean changes in oxy-hemoglobin (oxy-Hb) were evaluated while the participants performed the phonemic WFT.
Results: Healthy controls exhibited clear increases in oxy-Hb bilaterally throughout the medial to the lateral frontal cortices and the superior temporal areas during the WFT. In contrast, increases in oxy-Hb were mildly attenuated in EOD and severely attenuated in LOD in most channels. Subsequent analyses revealed that increases in oxy-Hb in LOD during the WFT was significantly poorer than in EOD in the left lateral portion of the cortex, including the dorsolateral prefrontal and the superior temporal areas. In addition, significant negative correlations were obtained between the age of onset and oxy-Hb, as well as between subcortical vascular changes and oxy-Hb in the lateral channels. These findings suggest that the higher the age of onset of depression, and the more prominent the vascular lesions, the greater the attenuation in lateral frontal and temporal activation, as indicated by NIRS.
Conclusions: Multichannel NIRS is useful for demonstrating attenuated functional activation in the left lateral prefrontal and temporal areas in LOD and, thus, for differentiating between LOD and EOD. The NIRS findings observed may have useful clinical implications for treatment-resistant LOD.