The mesopontine tegmentum in reward and aversion: From cellular heterogeneity to behaviour

The mesopontine tegmentum, comprising the pedunculopontine tegmentum (PPN) and the laterodorsal tegmentum (LDT), is intricately connected to various regions of the basal ganglia, motor systems, and limbic systems. The PPN and LDT can regulate the activity of different brain regions of these target systems, and in this way are in a privileged position to modulate motivated behaviours. Despite recent findings, the PPN and LDT have been largely overlooked in discussions about the neural circuits associated with reward and aversion. This review aims to provide a timely and comprehensive resource on past and current research, highlighting the PPN and LDT's connectivity and influence on basal ganglia and limbic, and motor systems. Seminal studies, including lesion, pharmacological, and optogenetic/chemogenetic approaches, demonstrate their critical roles in modulating reward/aversive behaviours. The review emphasizes the need for further investigation into the associated cellular mechanisms, in order to clarify their role in behaviour and contribution for different neuropsychiatric disorders. •Pedunculopontine nucleus (PPN) and laterodorsal tegmentum (LDT) play crucial roles in reward/aversion, influencing behaviours in neuropsychiatric disorders like addiction and depression.•PPN's involvement in motor functions and LDT's association with limbic functions suggest distinct roles in behavioural regulation.•Optogenetic studies reveal PPN and LDT's specific neuronal populations mediate diverse aspects of reward and aversion responses.•PPN deep brain stimulation shows potential in treating Parkinson's disease symptoms, impacting both motor functions and cognitive aspects like decision-making.•Future research should focus on PPN and LDT's microcircuits and their roles in reward-related processes and disorders.