Binge behaviour mechanism ‘switched off’ in brain study
The research results strongly suggest these pathways are linked to an impulse to overindulge, a challenge encountered by individuals addicted to food, alcohol and drugs.
The study focuses on the brain region known as the ventral pallidum (VP). Researchers believe it contributes to reward seeking by aiding in the upstream of signals from another region of the brain.
However, there is little research that has been carried out about how the VP pathway contributes to behavioural responses, when exposed to incentive cues.
Rat training
Scientists from Johns Hopkins University trained rats to expect a sugared drink when they pulled a lever in response to a siren or a beep. Brain activity within the VP was then monitored as the rats performed the task.
The team noticed a greater number of brain neurons lit up in response to the sound. The intensity of the neuronal response was so great that the team were able to predict how fast the animals would move to receive the sugar treat.
"External cues -- anything from a glimpse of powder that looks like cocaine or the jingle of an ice cream truck -- can trigger a relapse or binge eating," said lead author Dr Jocelyn Richard, a Johns Hopkins University post-doctoral fellow in psychological and brain sciences.
"Our findings show where in the brain this connection between environmental stimuli and the seeking of food or drugs is occurring."
The study may well be the first to more clearly define the relationship between VP cue responses and cue-induced reward seeking actions.
Previous studies have only revealed that VP neurons encode the value of primary reward as well as Pavlovian reward cues.
Optogenetics
Based on their rat observations, the team then used a technique called optogenetics that was able to suppress the VP’s neuron activity, when the rats heard the sugar cues.
As expected the inactive neurons made the rats less inclined to pull the sugar lever. Those that did were much slower in doing so.
“Optogenetic inhibition of VP neurons during DS presentations increases the latency of reward-seeking actions following the DS, as well as the probability of omissions.” the study noted.
“That ability to slow and calm the reaction to cues or triggers for binges could be key for people trying to moderate addictive behaviours,” Richard added.
"We don't want to make it so that people don't want rewards," she added. "We want to tone down the exaggerated motivation for rewards.
In determining the origin of the signals received by the VP that promote the intensity of the response, the team identified the basolateral amygdala and prefrontal cortex as likely candidates.
Input from these regions may be integrated with other signals to generate a notable response.
Future studies were recommended to determine what is specifically instructed by these inputs, and which targets were important for the generation of a response in reply to cues.
Source: Neuron
Published online ahead of print, doi:10.1016/j.neuron.2016.04.037
“Ventral Pallidum Neurons Encode Incentive Value and Promote Cue-Elicited Instrumental Actions.”
Authors: Jocelyn Richard, Frederic Ambroggi, Patricia Janak, Howard Fields
