COLUMNAR ORGANIZATION IN THE MIDBRAIN PERIAQUEDUCTAL GRAY - MODULES FOR EMOTIONAL EXPRESSION

Independent discoveries in several laboratories suggest that the midbr ain periaqueductal gray (FAG), the cell-dense region surrounding the m idbrain aqueduct, contains a Previously unsuspected degree of anatomic al and functional organization. This organization takes the form of lo ngitudinal columns of afferent inputs, output neurons and intrinsic in terneurons. Recent evidence suggests: that the important functions tha t are classically associated with the FAG - defensive reactions, analg esia and autonomic regulation - are integrated by overlapping longitud inal columns of neurons; and that different classes of threatening or nociceptive stimuli trigger distinct co-ordinated patterns of skeletal , autonomic and antinociceptive adjustments by selectively targeting s pecific FAG columnar circuits. These findings call for a fundamental r evision in our concept of the organization of the FAG, and a recogniti on of the special roles played by different longitudinal FAG columns i n co-ordinating distinct strategies for coping with different types of stress, threat and pain.