The use of EEGs (electroencephalograms) is now a commonplace, but d'Aquili and his colleagues used, over the last two years, brain scans on Buddhist monks in meditation. His intention was to compare the results with Carmelites in meditation in order to establish which parts of the brain are committed to particular tasks. On the basis of brain research, d'Aquili proposed far-reaching explanations of the ways in which ecstatic unitary states and theistic beliefs arise and take their characteristic forms.
Eugene d'Aquili was born in 1940, the son of first-generation immigrants from Italy to the United States. He was proud of his European ancestry, and maintained Italian traditions, especially at Christmas, in his home. There, he and his wife, Mary Lou, were a centre of generous, not to say gargantuan, hospitality.
He graduated from Villanova in Philosophy and Science in 1962. He went on to receive his MD at the University of Pennsylvania, winning the Priestley Prize for original scientific research.
He qualified as a psychiatrist (also at the University of Pennsylvania) and became a pioneer in cognitive therapy. He was a brilliant psychiatrist, and soon built up a large practice. But his heart was also in his research, and he received his PhD in Anthropology in 1979.
He and colleagues produced Biogenetic Structuralism in 1974, followed by The Spectrum of Ritual in 1979. D'Aquili did not write in popular style: the most accessible entry to his ideas is in his Brain, Symbol and Experience: toward a neurophenomenology of human consciousness (written with Charles Laughlin and John McManus, 1990), though he did write a lucid summary of his research for The Oxford Dictionary of World Religions (1997), based on an invited lecture given in London at Gresham College. With his colleague Andy Newberg, he was about to produce a new book with the tentative title Neurotheology.
Gene d'Aquili was a large man with a large sense of humour. His house, a refuge for many in psychiatric distress, was called appropriately Salus House. A smaller sign underneath it gave it his preferred name, Fantasyland. He had a prodigious memory and could recite by heart pages of Aquinas and an entire Latin hymnal. He was a faithful Catholic, though he had no time for what he regarded as the current follies of the Vatican. He lived a life of loyal dissent, writing letters of protest (in Latin) to Cardinal Ratzinger, yet always keeping the Easter Triduum in a private but passionate way.
Not surprisingly, his research was not reductionistic in the manner of the more ephemeral sociobiologists when they approach the subject of God. In his view, the naturalising of our religious behaviours in detailed brain research is not a comment, one way or the other, on what there is, outside our brains, waiting to be apprehended and known. He was, however, certain that the gene-protein process prepares us for religious, as much as it does for linguistic and sexual and many other, behaviours.
He altered the millennarian sign from its doom-laden "Prepare to meet thy God" to the far more exciting and inviting "Prepared to meet thy God". His wife, Mary Lou, died earlier this year, a blow from which he never recovered. He is survived by two daughters.
Eugene Guy d'Aquili, neuropsychologist: born Trenton, New Jersey 4 June 1940; married 1966 Mary Lou Adkins (died 1998; two daughters); died Philadelphia, Pennsylvania 22 August 1998.