Fear, anxiety and their disorders: past, present and future neural theories

This paper reviews the historical development of a two-dimensional (direction x distance (?)) neural model of defense. It begins with Miller’s (1944) analysis, and model, of approach, avoidance and conflict; adds Hinde’s (1966) ethological perspective and Flynn’s (1967) neural model of fear; and then considers Gray’s (1967, 1970) work linking barbiturate action to the hippocampus, McNaughton’s (1977) extension of this to other classes of anxiolytics, and Gray & McNaughton’s (1983) detailed behavioral comparison of anxiolytics and hippocampal lesions. This work led to Gray’s (1982) detailed model of the neuropsychology of anxiety. Rapoport’s (1989) model of the control of obsession by the cingulate cortex, and Ledoux’s (1994) model of the control of both fear and anxiety to the amygdala, suggested a more complex organisation of defense systems. McNaughton (1989) argued that evolutionary function defines an emotion, and Blanchard and Blanchard (1990) argued for its assessment via ethoexperimental analysis. Graeff (1994) then produced a neural model that mapped defensive distance to neural level, treating all anxiety as being at a greater defensive distance than fear. Seeing this, and the treatment of anxiety as due to uncertainty (which is inconsistent with Miller’s data), as being unsatisfactory, Gray and McNaughton (2000) and then McNaughton and Corr (2004) developed the two-dimensional model of defensive systems. This model is clearly incomplete at the present time and its links with neuroeconomics, personality, and stress and greater specification of frontal cortical contributions are suggested as directions for future development.