We performed stereotactic (ventralis intermedius), -CL (centralis lateralis) or -Vcpc (ventralis caudalis parvo-cellularis) thalamotomy in 19 patients with thalamic pain. The electrophysiological characteristics of the thalamus in patients with thalamic pain were analyzed. Patients were classified into non-thalamic and thalamic lesion groups on CT scan. Of 19 patients 13 were men (46-76 years) and 6 women (43-69 years); 11 showed cerebral infarct and 8 hemorrhage. Abnormal sensations including pain developed 1 month to 6 years (mean 11 months) after stroke. The clinical features of thalamic pain were referred to as “superficial pain” and “deep pain”. In the non-thalamic lesion group, we could usually recognize more deep than superficial pain, while, in the thalamic lesion group, superficial pain was predominant. We analyzed thalamic electrical activities [unitary spike discharges and background neural activity (BNA)], and compared them with those of parkinsonian patients. Furthermore, sensory neurons identified mainly in the thalamic sensory nucleus were studied with regard to the modality of peripheral natural stimulation, the distribution of peripheral receptive fields and the location of response sites in the thalamus.
Thalamic electrical activity was correlated with the state of thalamic lesions on CT scan and non-thalamic lesions, respectively. In the non-thalamic lesion group, thalamic BNA was relatively preserved in the ventral thalamus, but was not uniform in the nucleus (compared with that of parkinsonian patients). Furthermore, the peripheral receptive field of sensory (kinesthetic) neurons was predominantly the face or mouth area, deviating from standard thalamic topography in the nucleus. These findings suggest that functional change or reorganization in the thalamic sensory nucleus occurred in this group. In the thalamic lesion group, BNA decreased markedly in the ventral thalamus, particularly in the VC nucleus, and sensory (kinesthesic) neurons were rarely identified. Additionally, in about half the operated cases irregular burst discharges in and around the nucleus were frequently observed. It was suggested that the different character of thalamic pain, both deep and superficial, is associated with that of local pathophysiology in the thalamic sensory nucleus.

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Buddhaghosa introduces unorthodox views of anonymous ones in his Visuddhimagga (Vism) and other Pāli commentaries, while Dhammapāla in his sub-commentaries sometimes identifies them as the Abhayagirivihāravāsins’. It has been pointed that some of the views are found in the Vimuttimagga (), and consequently the has been considered to be the work of this school. Nevertheless, some scholars threw doubts about the relevance of the coincidence of the three facts, that is, the anonymous ones’ views known to Buddhaghosa, the Dhammapāla’s identification and the doctine in the . It seems, however, not fair if we, reputing that a theory is not enough proven, attempt to make an alternative explanation besed on a pile of hypotheses without verification and further investigation, while there is no rebuttal. It has to be more carefully weighed that if a sigle dhamma as a constituent element is different, it affects the basis of the elaborate system of the Theravāda Abhidhamma philosophy. In this sense, a placement of dhutaṅga (ascetic practice) in the Abhidhamma categories can be of great significance as one of the criteria to characterize the Abhayagirivihāravāsins.
Taking that into account, I reexamined the controversy over the definition of dhutaṅga in the Vism and the , and then considered how and why the Mahāvihāravāsins and the Abhayagirivihāravāsins classified it into a different category. Overviewing the references in the Vism and the and especially looking closely the passage in the : “[Dhutaṅga] should not be stated to be wholesome, unwholesome or indeterminate,” one may challenge their concordance. However, there is a further crucial evidence to link the to the Abhayagirivihāravāsins, that in the dhutaṅga is explicitly mentioned in the list of concept (paññatti) which has been unknown to the scholars.
Looking into the Pāli canon, we often meet ascetic practitioners who are of evil wishes, pursue a reputation, and so on. There are philosophical gaps between the Vism and Pāli commentaries, too, regarding the understanding of dhutaṅga. Furthermore, we notice that the definition of dhutaṅga in the Vism was not given by Buddhaghosa, but was quoted from “Aṭṭhakathā” as an old commentary. It seems reasonable to suppose that discussions as to dhutaṅga arose in the Sīhaḷa-sources of Pāli commentaries and bhāṇakas (reciters), and that these two schools built their definitions of dhutaṅga, receiving the preceding discussions and trying to refuse the view that it can be unwholesome.

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