Representations of motivational drives in mesial cortex, medial thalamus, hypothalamus and midbrain

We propose that neural representations of motivational drives, including sexual desire, hunger, thirst, fear, power-dominance, the motivational aspect of pain, the need for sleep, and nurturance, are represented in four areas in the brain. These are located in the medial hypothalamic/preoptic area, the periaqueductal gray matter (PAG) in the midbrain/pons, the midline and intralaminar thalamic nuclei, and in the anterior part of the mesial cortex, including the medial prefrontal and anterior cingulate areas. We attempt to determine the locations of each of these representations within the hypothalamus/preoptic area, periaqueductal gray and cortex, based on the available literature on activation of brain structures by stimuli that evoke these forms of motivation, on the effects of electrical and chemical stimulation and lesions of candidate structures, and on hodological data. We discuss the hierarchical organization of the representations for a given drive, outputs from these representations to premotor structures in the medulla, caudate-putamen, and cortex, and their contributions to involuntary, learned-sequential (operant) and voluntary behaviors.