Brain complexity: roles of dopamine neurons (Introduction)

by David Turell , Monday, April 25, 2016, 18:51 (3134 days ago) @ dhw

The brain is more than just electrical signals. Chemicals like dopamine play important and at times differing roles:-http://medicalxpress.com/news/2016-04-dopamine-neurons-role-movement.html-"Princeton University researchers have found that dopamine - a brain chemical involved in learning, motivation and many other functions - also has a direct role in representing or encoding movement. -***-"The researchers used a new, more precise technique to record the activity of dopamine neurons at two regions within a part of the brain known as the striatum, which oversees action planning, motivation and reward perception. The researchers found that while all of the neurons carried signals needed to learn and plan movement, one of the nerve bundles, the one that went to the region called the dorsomedial striatum, also carried a signal that could be used to control movements.-***-"The new study affirmed the role of dopamine in reward-based learning, but also found that in the dorsomedial striatum, dopamine neurons can play a direct role in movement. The researchers used a method for measuring neuron activity at very precise locations in the brain. They measured the activity at the ends of neurons - the terminals where dopamine is released into the junction, or synapse, between two cells - in two locations in the striatum: the nucleus accumbens, known to be involved in processing reward, and the dorsomedial striatum, known for evaluating and generating actions.-***-"The researchers found that the dopamine neurons that innervate the nucleus accumbens and the dorsomedial striatum did indeed encode reward-prediction cues, which is consistent with previous findings. But they also found that in the dorsomedial striatum, the dopamine neurons carried information about what actions the animal is going to take.-"'This idea was that dopamine neurons carry this reward-prediction error signal, and that could indirectly affect movement or actions, because if you don't have this, you won't correctly learn which actions to perform," Witten said. "We show that while this is true, it is certainly not the whole story. There is also a layer where dopamine is directly coding movement or actions."-***-"The study addresses the more general question of how dopamine can be involved in so many functions in the brain, Witten said. "We think that some of the way that dopaminergic neurons achieve such diverse functions in the brain is by having specific roles based on their anatomical target."-***-"'This study by the Witten lab elegantly shows that the activity of some dopamine neurons is modulated by the direction of motion," Uchida said. "More importantly, they found some of the clearest evidence indicating the heterogeneity of dopamine neurons: A specific population of dopamine neurons projecting to the dorsomedial striatum encodes movement direction more so compared to another population projecting to the ventral striatum.'"-***-"Uchida continued, "A similar phenomenon has also been reported in an independent study in non-human primates (Kim, et al., Cell, 2015), suggesting that the Witten lab finding is more universal and not specific to mice."-Comment: Both dopamine and the neurotransmitters at synapses can change concentrations to have differing effects, as can various hormones arriving in the blood (i.e., adrenalin)