Biology subjects

Amarante, L. M.

Publications and source records attributed to Amarante, L. M..

3 recordsLinked to original sources

bioRxiv2025

Cholinergic-dependent dopamine signals in mouse dorsal striatum are regulated by frontal but not sensory cortices

Everyday decisions depend on linking sensory stimuli with actions and outcomes. The striatum supports these sensorimotor associations through dopamine-dependent plasticity. Thus, the timing and magnitude of dopamine release is critical for learning. Recent work has characterized a local striatal microcircuit in which cholinergic interneurons (CINs) modulate dopamine release via acetylcholine activation of nicotinic receptors on dopamine axons. Here, we show that visual stimuli evoke dopamine responses in the dorsomedial striatum through this cholinergic-dependent mechanism. Using anatomical and functional methods to identify which pathways elicit these signals, we found that visual and auditory cortices that project to the dorsomedial striatum lack robust connectivity to CINs and were unable to drive cholinergic-dependent dopamine release. In contrast, frontal cortical regions, including the prelimbic and anterior cingulate cortices, strongly recruited CINs and acetylcholine, producing robust dopamine release both ex vivo and in vivo. These frontal corticostriatal projections are activated by visual stimuli, representing a possible pathway by which visual information reaches the dorsomedial striatum to evoke dopamine. These findings reveal a fundamental distinction between sensory and frontal cortical inputs to the striatum, demonstrating that only the latter evoke cholinergic-dependent dopamine signaling. This work establishes a framework for understanding how cortical circuits shape striatal dopamine to support reinforcement learning.

neuroscience↗

bioRxiv2020

Rhythmic activity in the medial and orbital frontal cortices tracks reward value and the vigor of consummatory behavior

This study examined how the medial frontal (MFC) and orbital frontal (OFC) cortices process reward information. We simultaneously recorded local field potentials in the two areas as rats consumed liquid sucrose rewards. Both areas exhibited a 4-8 Hz "theta" rhythm that was phase locked to the lick cycle. The rhythm tracked shifts in sucrose concentrations and fluid volumes, demonstrating that it is sensitive to differences in reward magnitude. The coupling between the rhythm and licking was stronger in MFC than OFC and varied with response vigor and absolute reward value in the MFC. Spectral analysis revealed zero-lag coherence between the cortical areas, and found evidence for a directionality of the rhythm, with MFC leading OFC. Our findings suggest that consummatory behavior generates simultaneous theta range activity in the MFC and OFC that encodes the value of consumed fluids, with the MFC having a top-down role in the control of consumption.

neuroscience↗

bioRxiv2017

Rhythmic Activity In The Medial Frontal Cortex Encodes Relative Reward Value

Rodents lick to consume fluids. The reward value of ingested fluids is likely to be encoded by neuronal activity entrained to the lick cycle. Here, we investigated relationships between licking and reward signaling by the medial frontal cortex [MFC], a key cortical region for reward-guided learning and decision-making. Multi-electrode recordings of spike activity and field potentials were made in male rats as they performed an incentive contrast licking task. Rats received access to higher and lower value sucrose rewards over alternating 30 sec periods. They learned to lick persistently when higher value rewards were available and to suppress licking when lower value rewards were available. Spectral analysis of spikes and fields revealed evidence for reward value being encoded by the strength of phase-locking of a 6-12 Hz theta rhythm to the rats lick cycle. Recordings during the initial acquisition of the task found that the strength of phase-locking to the lick cycle was strengthened with experience. A modification of the task, with a temporal gap of 2 sec added between reward deliveries, found that the rhythmic signals persisted during periods of dry licking, a finding that suggests the MFC encodes either the value of the currently available reward or the vigor with which rats act to consume it. Finally, we found that reversible inactivations of the MFC in the opposite hemisphere eliminated the encoding of reward information. Together, our findings establish that a 6-12 Hz theta rhythm, generated by the rodent medial frontal cortex, is synchronized to rewarded actions.\n\nSignificance StatementThe cellular and behavioral mechanisms of reward signaling by the medial frontal cortex [MFC] have not been resolved. We report evidence for a 6-12 Hz theta rhythm that is generated by the MFC and synchronized with ongoing consummatory actions. Previous studies of MFC reward signaling have inferred value coding upon temporally sustained activity during the period of reward consumption. Our findings suggest that MFC activity is temporally sustained due to the consumption of the rewarding fluids, and not necessarily the abstract properties of the rewarding fluid. Two other major findings were that the MFC reward signals persist beyond the period of fluid delivery and are generated by neurons within the MFC.

neuroscience↗