Spine dynamics in the brain, mental disorders and artificial neural networks

The basal ganglia are a chain of subcortical nuclei that facilitate action selection. Two striatal projection systems--so-called direct and indirect pathways--form the functional backbone of the basal ganglia circuit. Twenty years ago, investigators proposed that the striatum's ability to use dopamine (DA) rise and fall to control action selection was due to the segregation of D(1) and D(2) DA receptors in direct- and indirect-pathway spiny projection neurons. Although this hypothesis sparked a debate, the evidence that has accumulated since then clearly supports this model. Recent advances in the means of marking neural circuits with optical or molecular reporters have revealed a clear-cut dichotomy between these two cell types at the molecular, anatomical, and physiological levels. The contrast provided by these studies has provided new insights into how the striatum responds to fluctuations in DA signaling and how diseases that alter this signaling change striatal function.

Summary Schizophrenia is a complex, heterogeneous behavioural and cognitive syndrome whose origins appear to lie in genetic and/or environmental disruption of brain development. Dysfunction of dopaminergic neurotransmission appears to contribute to the genesis of psychotic symptoms but the evidence also points to a more widespread and variable involvement of brain areas and circuits. There is emerging evidence that disturbances of synaptic function might underlie abnormalities of neuronal connectivity possibly involving interneurons, but the precise nature, location and timing of these events is uncertain. Current treatment consists largely in the administration of antipsychotic drugs combined with psychological therapies, social support and rehabilitation, but there is a pressing need for more effective treatments and for services to be delivered more effectively. Progress in understanding the disorder has been great in recent years with advances in genomics, epidemiology and neuroscience, and the opportunities for further scientific advance are great: but so are the challenges.