What do the neurosciences tell us about anxiety disorders? A comment.

EDITORIAL What do the neurosciences tell us about anxiety disorders? A comment 1 Defensive responses range from simple reflex withdrawal and accompanying physiological reactions present from invertebrates to humans, to far more intricate emotional behaviour typical of higher taxa. Is there some order in the numerous circuits and neuroregulators that are implicated in the acquisition and expression of many different forms of defensive behaviour across phyla and in the human clinical syndromes in which they appear? The sheer complexity of the problem has defied attempts to integrate such knowledge with that of the various anxiety syndromes in meaningful detail. The task, however, is no longer altogether hopeless. The same four basic strategies of defensive behaviour-withdrawal, immobility, aggressive defence, and deflection of attack (Marks, 1986)-are found in both invertebrates and vertebrates, although only withdrawal and immobility seem to be involved in phobic and obsessive-compulsive disorders. Also common across phyla are the basic forms of learning such as habituation, sensitization, and classical and instrumental conditioning. Some insights have come from animal studies of forms of behaviour like passive and active avoidance, escape, freezing, immobility and startle. Further knowledge has accrued from experiments with forms of defensive learning involving classical conditioning, sensitization and habituation. Information about such behaviour and processes has aided our understanding of the modes of action of behavioural treatment (Marks, 1986) and anxiolytic drugs (Gray, 1982). It is, of course, a cliche that similar forms of behaviour have repeatedly evolved across taxa independently of one another by different mechanisms (convergence). On the other hand, conservation of evolutionary mechanisms has been found repeatedly. Is there any reason to believe that some of the shared defensive strategies and ways in which they are modified by learning are mediated by common physiological mechanisms? Are there enough points in common between invertebrates and vertebrates to make this likely? Some organizing principles are, in fact, emerging. First, in vertebrates 50 years of research have produced convincing evidence that several deep structures in the brain are involved in fearful withdrawal and immobility. Modification of withdrawal in both aplysia and mammals is mediated by changes not at the peripheral sensory receptor in skin or muscle, but central to the body of the sensory neuron-among others, at the synapse of the sensory neuron with an interneuron and/or a motor neuron in aplysia, such synapses being in the spinal cord and brain in mammals. The deep mammalian structures related …