The limbic system (also known as the paleomammalian brain) is a collection of brain structures located in the middle of the brain described by neuroscientist Paul MacLean as part of his triune brain model. It was first defined by Paul Broca in the nineteenth century as the structures between the cerebral hemisphere and the brainstem (i.e., the limbus, or border of the brain). The limbic system is not a discrete system itself but rather a collection of structures—anatomically related but varying greatly in function. The term has been in use for about 70 years and does suggest a functionally unified system, but as this is not the case some neuroscientists believe it should be abandoned. Contemporary neuroscience conceives functional brain activity from the perspective of neural networks that run throughout the brain and described as the salience network, or the executive control network, or the default mode network, to name a few major functional networks.
If we were to stay with the old term we can think of the limbic system as the centre for emotional responsiveness, motivation, memory formation and integration, olfaction, and the mechanisms to keep ourselves safe. These are broad strokes to be sure, which is not to suggest that the neo-cortex is not involved in these functions, but these are the focal activities of the limbic system. The amygdala, hippocampus, and hypothalamus are considered the main limbic structures of clinical relevance to the practising psychotherapist. There is also the very important hub of information transfer, the thalamus, which feeds the limbic system with sensory input.
The basal ganglia, a set of subcortical structures located near the thalamus and hypothalamus, are also included in the limbic system and are involved in intentional movements. It is important to note that inadequate dopamine supply to the basal ganglia may affect posture and movement, leading to the symptoms of Parkinson’s disease. The limbic system is closely connected to the prefrontal cortex, and it is this prefrontal–limbic connection that is strengthened when practising mindfulness. The functional relevance of the limbic system to psychotherapy is obvious—as affect, memory, sensory processing, time perception, attention, consciousness, autonomic control, motor behaviour, and more are all mediated in and through this collection of structures.