Summary: A new study in mice identifies dopamine release along a specific brain circuit as the signal that helps the brain extinguish fear. Rather than merely suppressing fear, dopamine from the ventral tegmental area (VTA) activates reward-responsive neurons in the basolateral amygdala (BLA) to drive a positive learning process that replaces fear memory. Disruption of this dopamine pathway impairs the ability to unlearn fear, with important implications for understanding and treating anxiety and post-traumatic stress disorder (PTSD).
The findings point to a precise neural mechanism that restores calm when it works and may prolong anxiety when it fails. By clarifying how dopamine functions as a teaching signal for fear extinction, the research highlights potential targets for therapies aimed at fear-related disorders.
Key Facts:
- Teaching signal: Dopamine released from the VTA activates distinct amygdala neurons that promote fear extinction.
- Reward-based learning: Extinguishing fear is an active, positive learning process driven by the brain’s reward circuitry rather than simple suppression of the original fear memory.
- Therapeutic potential: The pBLA–VTA dopaminergic pathway and dopamine receptor signaling in specific amygdala cells could be targets for new interventions for PTSD and anxiety.
Source: Picower Institute at MIT
Dangers arrive, but they also pass—and when they do, the brain issues an “all-clear” teaching signal that helps extinguish fear.
New experiments from neuroscientists at MIT show that this all-clear signal is dopamine released along a defined interregional circuit between the ventral tegmental area and discrete cell populations in the basolateral amygdala. The work identifies a circuit-level mechanism relevant to adaptive behavior and to the pathology of persistent anxiety and PTSD.
According to Michele Pignatelli di Spinazzola, co-author of the study from Susumu Tonegawa’s lab at the Picower Institute for Learning and Memory, dopamine is essential to initiate fear extinction. The lab’s prior work showed that fear acquisition and fear extinction result from opposing populations of neurons in the anterior and posterior basolateral amygdala.
When a mouse learns that a context is dangerous (for example, receiving foot shocks in an enclosure), fear is encoded by Rspo2-expressing neurons in the anterior BLA (aBLA). When the mouse subsequently learns the context is safe because the anticipated shocks no longer occur, a new extinction memory forms in Ppp1r1b-expressing neurons in the posterior BLA (pBLA). Those pBLA neurons are also involved in reward processing, which explains why relief feels rewarding when a predicted danger fails to materialize.
The new study, led by Xiangyu Zhang and Katelyn Flick and published in the Proceedings of the National Academy of Sciences, asked what instructs pBLA neurons to form extinction memories. The authors combined circuit tracing, receptor profiling, dopamine activity recordings, and projection-specific manipulations to test whether VTA dopaminergic input provides that instruction.
Circuit tracing revealed a topographic organization: dopaminergic neurons in anterior and lateral VTA regions target Rspo2 aBLA neurons, while dopaminergic neurons in central and posterior VTA regions preferentially target Ppp1r1b pBLA neurons. Consistent with this input pattern, the Ppp1r1b cells express higher levels of D1-type dopamine receptors than the Rspo2 cells.
To observe dopamine signaling during learning, the team used fiber photometry to monitor dopamine in the amygdala while mice underwent a three-day behavioral protocol. On day one mice received foot shocks in the context; on day two they returned without shocks and gradually ceased freezing; on day three extinction memory was tested. During shocks, dopamine responses were stronger at Rspo2-related circuits; crucially, when the anticipated shocks failed to appear and mice relaxed, dopamine signals shifted to the Ppp1r1b extinction neurons. Moreover, mice that extinguished fear most effectively exhibited the largest dopamine signals in those pBLA neurons.
Causal evidence for dopamine’s role
To test causality, researchers used optogenetics to manipulate VTA dopamine axons in the BLA. Silencing VTA dopaminergic inputs to the pBLA impaired extinction, while activating those inputs accelerated extinction. Surprisingly, activating VTA dopaminergic inputs to the aBLA reinstated fear even without new shocks, interfering with extinction. Complementary receptor manipulations showed that boosting D1 receptor expression in Ppp1r1b neurons enhanced extinction and impaired fear recall, whereas knocking down D1 receptors in Ppp1r1b cells reduced extinction. In Rspo2 cells, reducing receptor levels decreased freezing behavior.
Together, these manipulations demonstrate that VTA dopamine signaling bidirectionally controls fear and extinction through distinct activity patterns and receptor expression in separate BLA neuron populations.
The authors emphasize that while this VTA–BLA circuit provides a specific “teaching signal” for extinction learning, fear extinction is a distributed brain process. Still, this circuit represents a key node for translational approaches. Targeting dopaminergic modulation in the pBLA or manipulating circuit-specific signaling could inform new therapies for generalized anxiety and PTSD.
The study lists Susumu Tonegawa, Michele Pignatelli di Spinazzola, Xiangyu Zhang, Katelyn Flick, Marianna Rizzo and others as contributors. Funding and support came from the RIKEN Center for Brain Science, the Howard Hughes Medical Institute, the Freedom Together Foundation, and The Picower Institute for Learning and Memory.
About this dopamine and PTSD research news
Author: David Orenstein
Source: Picower Institute at MIT
Contact: David Orenstein – Picower Institute at MIT
Image credit: Neuroscience News
Original research (open access): “Dopamine induces fear extinction by activating the reward-responding amygdala neurons” by Susumu Tonegawa et al., published in Proceedings of the National Academy of Sciences (PNAS).
Abstract
Dopamine induces fear extinction by activating the reward-responding amygdala neurons
Extinction of conditioned fear responses is vital for adaptive behavior, and impaired extinction is a hallmark of anxiety disorders such as PTSD. Extinction occurs when animals form a new memory that suppresses the original fear memory. This new memory is encoded in the reward-responsive posterior BLA by Ppp1r1b+ neurons, which suppress activity of Rspo2+ fear-responding neurons in the anterior BLA. The teaching signal that instructs formation of extinction memory in Ppp1r1b+ neurons had been unclear. This study demonstrates that VTA dopaminergic signaling drives fear extinction in distinct BLA populations. BLA fear and extinction neurons receive topographically distinct VTA inputs and express different dopamine receptor levels. Fiber photometry shows dopamine activity is time-locked to the cessation of freezing in extinction neurons and correlates with extinction learning. Projection-specific optogenetic manipulations reveal that activating VTA projections to BLA reward neurons accelerates extinction, whereas activating projections to BLA fear neurons impairs extinction. Overall, dopaminergic activity bidirectionally controls fear extinction through different patterns of activity at BLA fear and extinction neurons.