Depression consists of a heterogenous set of symptoms such as low mood and blunted emotion known as anhedonia. A brain area extensively reported to be involved in depression is the subgenual anterior cingulate cortex area 25, which seems to be overactive in depression. Recently it has been shown that overactivation of area 25 in marmosets led to anticipatory and motivational anhedonia as measured by blunted cardiovascular responses and behavioural arousal in an appetitive Pavlovian task, and reduced willingness to work in a Progressive Ratio task respectively.
In this study the role of area 25 in motivation was further investigated by inactivating this region by infusing GABA A/B agonists in cannulated marmosets on the progressive ratio task. We show that inactivation of area 25 increased total responses. However, there was also an increase in licking behaviour outside of reward delivery. A follow-up sucrose preference test showed that inactivating this brain area also led to an increase in sucrose consumption.
Overall the findings indicate that area 25 inactivation increases motivation as measured by the increased breakpoint, but also promotes a consummatory behaviour. Dissecting the network related to these changes in both motivation and consummatory behaviour will be key to understanding the role of the subgenual cingulate cortex in mood disorders. We hypothesise that whilst the increased breakpoint may be related to subgenual interactions with the nucleus accumbens, increased consummatory licking may be related instead to interactions with the hypothalamus.