The abnormalities were located not only in visual cortex, but also in the DMN, limbic system, and motor and sensory networks. This alteration of brain function is similar to that in other neurodegenerative diseases. Among these areas, the DMN is primarily concerned. The PCC, MTG, medial prefrontal cortex (MPFC), and IPL are major regions of the DMN. The PCC is considered the central node in the DMN, and the decreased ALFF of this area is tightly linked to AD progression in previous studies.
42–44 The hypometabolism and atrophy of medial temporal lobe in AD progression was also revealed.
45,46 In this study, significantly decreased fALFF values in the left PCC and right MTG were observed in POAG patients, and those in the right MFG and left IPL were significantly increased in POAG patients. These results were not totally the same as those of prior AD research, which showed decreased spontaneous neural activity in MPFC.
44,47 The difference could be due to differing progression of neurodegeneration. At an early stage of AD, the posterior cortical regions were the first to be affected, and other regions, including frontal cortex, were vulnerable at lower levels and later stages.
45 With respect to our results, the increased activity in anterior DMN areas could be interpreted as a compensatory process for decreased activity in posterior DMN areas.
48 Similar alterations in healthy elderly persons, mild cognitive impairment, and neuromyelitis optica have also been interpreted as compensatory.
48–50 In POAG patients, a significant decrease in fALFF was shown in the right limbic lobe while a significant increase of fALFF was shown in the right MCC. As parts of the limbic system, these areas are primarily responsible for emotion, behavior, and long-term memory. Although POAG patients have been reported to experience higher levels of emotional instability than controls,
9 it was unfortunate that the patients recruited in this study did not undergo psychological testing to confirm the correlation between the psychological abnormalities and the fALFF values. Moreover, in patients with POAG, a reduction of spontaneous neural activity could also be found in some motor and sensory cortices, including the left PCG and left precentral gyrus. The PCG and precentral gyrus constitute the motor and sensory networks
51; and in previous studies, this network was reported to be associated with PVA spontaneous activity.
19 Furthermore, it was reported that this network would have decreased functional connectivity and reduced regional homogeneity in patients with POAG.
20,34 Our results provided further evidence for the alteration in these areas.