The rat medial frontal cortex controls pace, but not breakpoint, in a progressive ratio licking task.

Abstract

1 2 3 4 5 6 7 8 MEDIAL FRONTAL CORTEX AND PROGRESSIVE RATIO PERFORMANCE 2 AbstractThe medial frontal cortex (MFC) is crucial for selecting actions and evaluating their outcomes.Outcome monitoring may be triggered by rostral parts of the MFC, which contain neurons that are modulated by reward consumption and are necessary for the expression of relative reward value. Here, we examined if the MFC further has a role in the control of instrumental licking.We used a progressive ratio licking task in which rats had to make increasing numbers of licks to receive liquid sucrose rewards. We determined what measures of progressive ratio performance are sensitive to value by testing rats with rewards containing 0-16% sucrose. We found some measures (breakpoint, number of licking bouts) were sensitive to sucrose concentration and others (response rate, duration of licking bouts) were not. Then, we examined the effects of reversibly inactivating rostral (medial orbital) and caudal (prelimbic) parts of the MFC. We were surprised to find that inactivation had no effects on measures associated with value (e.g. breakpoint). Instead, inactivation altered behavioral measures associated with the pace of task performance (response rate and time to break). These effects depended on where inactivations were made. Response rates increased and time to break decreased when the caudal prelimbic area was inactivated. By contrast, response rates decreased and the time to break increased when the rostral medial orbital cortex was inactivated. Our findings suggest that the medial frontal cortex has a role in maintaining task engagement, but not in the motivational control of action, in the progressive ratio licking task.Inhibition is a classic interpretation of orbitofrontal function (Dias et al., 1996).However, more recent studies have emphasized a role for the medial orbital areas in predictions and evaluations of behavioral outcomes (Rudebeck & Murray, 2014;Rudebeck et al., 2017) and inferences based on learned associations between actions and outcomes (Bradfield et al., 2015).As such, disruptions of medial orbital control should reduce, not increase, breakpoints, as is also 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 cues signaling reward delivery, and the method, spatial extent, and cell type affected by the brain perturbations (lesion, muscimol, chemogenetics, optogenetics). Our findings on breakpoint are similar to three published studies. Kheramin et al. (2005), Schweimer & Hauber (2005), and Gourley et al. (2010) found no effects of lesions in three different cortical areas, two different actions, two different species, and very different levels of training. The Kheramin study used rats, required lever pressing, and lesioned the ventral orbital area after 60 training sessions. The Schweimer study also used rats, required lever pressing, and lesioned the perigenual prelimbic and cingulate after 6 training sessions. The Gourley study used

Coherent theta activity in the medial and orbital frontal cortices encodes reward value

“…The electrophysiological results from the Blocked-Interleaved Task and Three Reward Task suggest that MFC and OFC, while showing similar results overall, may be contributing to processing reward information in different ways. In accord with a previous theory on proposed MFC and OFC functions Dickinson, 1998, Balleine andDickinson, 2000;Schoenbaum et al, 2009;Sul et al, 2011;Passingham and Wise, 2012), MFC activity may be acting to maintain and optimize licking behavior in an action-centric manner, as reflected in measures such as the licking rate, a measure associated with vigor and sensitive to inactivation of the same cortical area in a progressive ratio licking task (Swanson et al, 2019). By contrast, OFC activity generally reflected differences in reward value, perhaps due to the different sensory properties of the fluids (Gutierrez et al, 2006), and was not sensitive to licking rate (vigor) or task engagement (total licks).…”

Noradrenergic Regulation of Two-Armed Bandit Performance

“…Rats were allowed 7 days of recovery before returning to behavioral testing. Intracerebral drug infusions were done under isoflurane anesthesia as in previously reported (Swanson et al, 2019). To acclimate the rats to testing after gas anesthesia, they were anesthetized for 10 minutes one hour prior to testing for 1-2 sessions.…”

Involvement of the rodent prelimbic and medial orbitofrontal cortices in goal‐directed action: A brief review

“…This procedure is quite established (Hodos, ), so a rich literature exists, and it has multiple other advantages. It can be conducted such that the organism is required to make minimal movement, advantageous for certain procedural and data interpretation considerations (discussed by Swanson et al, ). Further, a progressive ratio task can be devoid of explicit Pavlovian stimuli, encouraging rodents to utilize action–outcome strategies.…”

“…It is important to note that in rodents familiar with the progressive ratio task or extensively trained in other food‐reinforced procedures, mOFC inactivation has the opposite effect, decreasing responding (Gardner et al, ; Swanson et al, ). Whether this outcome is attributable to disruption in value memory retrieval is unclear, and potentially instead explained by the notion that another function of the mPFC—including the mOFC—is to help keep organisms “on task,” maintaining responding over long delay periods (discussed in Swanson et al, ). The mOFC may help to keep organisms “on task” via connections with the ventral striatum and parts of the hypothalamus that control behavioral activation and autonomic and homeostatic processes (Swanson et al, ).…”

“…Whether this outcome is attributable to disruption in value memory retrieval is unclear, and potentially instead explained by the notion that another function of the mPFC—including the mOFC—is to help keep organisms “on task,” maintaining responding over long delay periods (discussed in Swanson et al, ). The mOFC may help to keep organisms “on task” via connections with the ventral striatum and parts of the hypothalamus that control behavioral activation and autonomic and homeostatic processes (Swanson et al, ). For instance, the mOFC modulates nucleus accumbens shell‐elicited feeding, greatly potentiating food intake (Richard & Berridge, ).…”