Biology subjects

Janak, P. H.

Publications and source records attributed to Janak, P. H..

3 recordsLinked to original sources

bioRxiv2018

Setting the occasion for incentive motivation: implications for addiction

The context in which reward-paired cues are encountered sets the occasion for appropriate reward-seeking but may also spur inappropriate behaviors such as the renewal of drug-seeking. The psychological processes underlying occasion setting remain unclear as contexts are diffuse and difficult to isolate from other stimuli. To overcome this, we modeled a context as a phasic and discrete event - an occasion setter - which allowed for control over its presentation and influence on cue-driven reward-seeking. This allowed us to directly assess how occasion setters, like contexts, regulate the predictive and motivational significance of Pavlovian cues. Male rats (n=50) were trained in a Pavlovian paradigm where the presentation of an ambiguous conditioned stimulus was reinforced only if preceded by an occasion setting cue. We assessed the motivational value of the occasion setter and conditioned stimulus alone or in combination using conditioned reinforcement. Rats showed enhanced conditioned approach to the reward port during the reward-adjacent conditioned stimulus when it was preceded by the occasion setter. When allowed the opportunity, rats responded more to obtain presentations of the conditioned stimulus in combination with the occasion setter than the conditioned stimulus alone. Critically, rats also worked to obtain presentations of the occasion setter alone more than the conditioned stimulus, and this was resistant to manipulations of the value of the occasion setter. We conclude that occasion setting can act via incentive motivational mechanisms and that, apart from resolving predictive information about ambiguous reward-paired cues, occasion setters themselves generate states of appetitive motivation that can facilitate reward-seeking.

neuroscience↗

bioRxiv2017

Phasic Activation of Ventral Tegmental, but not Substantia Nigra, Dopamine Neurons Promotes Model-Based Pavlovian Reward Learning

Dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra (SNc) encode reward prediction errors (RPEs) and are proposed to mediate error-driven learning. However the learning strategy engaged by DA-RPEs remains controversial. Model-free associations imbue cue/actions with pure value, independently of representations of their associated outcome. In contrast, model-based associations support detailed representation of anticipated outcomes. Here we show that although both VTA and SNc DA neuron activation reinforces instrumental responding, only VTA DA neuron activation during consumption of expected sucrose reward restores error-driven learning and promotes formation of a new cue[->]sucrose association. Critically, expression of VTA DA-dependent Pavlovian associations is abolished following sucrose devaluation, a signature of model-based learning. These findings reveal that activation of VTA-or SNc-DA neurons engages largely dissociable learning processes with VTA-DA neurons capable of participating in model-based predictive learning, while the role of SNc-DA neurons appears limited to reinforcement of instrumental responses.

neuroscience↗

bioRxiv2017

Long-Lasting Contribution Of Dopamine In The Nucleus Accumbens Core, But Not Dorsal Lateral Striatum, To Sign-Tracking

The attribution of incentive salience to reward-paired cues is dependent on dopamine release in the nucleus accumbens core. These dopamine signals conform to traditional reward-prediction error signals and have been shown to diminish with time. Here we examined if the diminishing dopamine signal in the nucleus accumbens core has functional implications for the expression of sign-tracking, a Pavlovian conditioned response indicative of the attribution of incentive salience to reward-paired cues. Food-restricted male Sprague-Dawley rats were trained in a Pavlovian paradigm in which an insertable lever predicted delivery of food reward in a nearby food cup. After 7 or 14 training sessions, rats received infusions of saline, the dopamine antagonist flupenthixol (100 mM), or the GABA agonists baclofen and muscimol (0.5 mM baclofen/0.05 mM muscimol) into the nucleus accumbens core or the dorsal lateral striatum. Dopamine antagonism within the nucleus accumbens core attenuated sign-tracking, whereas reversible inactivation did not affect sign-tracking but increased non-specific food cup checking behaviors. Neither drug in the dorsal lateral striatum affected sign-tracking behavior. Critically, extended training did not alter these effects. Though extended experience with an incentive stimulus may reduce cue-evoked dopamine in the nucleus accumbens core, this does not alter the function of dopamine in this region to promote Pavlovian cue approach nor result in the recruitment of dorsal lateral striatal systems for this behavior. These data support the notion that dopamine within the mesoaccumbal system, but not the nigrostriatal system, contributes critically to incentive motivational processes independent of the length of training.\n\nAbbreviations

neuroscience↗