Summary: This study reveals how a specific neural circuit allows prey animals to use the sounds—or the sudden absence of sound—produced by other animals to detect danger and produce defensive behavior.
Source: PLOS
Overview: Researchers have identified a previously uncharacterized neural circuit that enables rats to interpret silence as a danger cue and to mount defensive responses. Published May 12, 2020 in the open-access journal PLOS Biology, the study led by Marta Moita at the Champalimaud Centre for the Unknown (Portugal) and colleagues clarifies how auditory information and its cessation are processed by the brain to drive survival behaviors.
Many animals rely on acoustic cues produced by conspecifics to detect threats in the environment. Past work has emphasized active alarm signals such as calls or foot stomping. This study focuses on a passive but ecologically important cue: silence. When a rat perceives imminent danger, it commonly freezes—becoming motionless and quiet. Other rats detect this absence of movement-related sound and interpret the silence as evidence of danger, leading them to freeze as well.
Until now, the neural pathways that allow the brain to detect and respond to such natural auditory cues and their abrupt offset were not well understood. To address this, Moita and colleagues tested which brain regions are necessary for rats to display defensive freezing in response to the silence produced by another rat that had been exposed to foot shocks.
Using targeted inactivation of multiple brain regions, the researchers found that disabling any one of three areas reduced rats’ tendency to freeze when they heard the silence generated by a conspecific that had been shocked. The circuit spans key auditory-processing areas and a core emotional center: the dorsal subnucleus of the medial geniculate body (MGD), the ventral area of the auditory cortex (VA), and the lateral amygdala (LA). These regions form a pathway that appears particularly important for detecting the offset of ongoing sounds and translating that information into a defensive behavioral response.
Specifically, the findings suggest that the auditory offset pathway—neuronal circuits specialized to detect when sounds stop—plays a central role in interpreting natural silence as a threat signal. The inclusion of the lateral amygdala in this circuit highlights how sensory processing and emotional valuation are integrated to produce rapid, adaptive behaviors like freezing.
Beyond revealing the anatomical components of this mechanism, the study advances our understanding of social and sensory factors that shape defensive behavior. By identifying how passive cues such as silence are encoded and relayed through thalamic, cortical, and amygdalar regions, the research points to a broader framework for how animals use the behavior of others to inform their own responses to danger.
Implications: These results are important for neuroscience and behavioral ecology because they: (1) demonstrate that the sudden absence of sound is a biologically relevant danger cue processed by a distinct neural pathway; (2) connect auditory processing centers with the amygdala to show how sensory offsets can trigger emotional and motor outputs; and (3) open avenues for future studies on how social auditory cues modulate threat perception and decision-making.
Funding and support: The work was supported by the Champalimaud Foundation and infrastructure support for the Champalimaud Vivarium through the Lisboa2020 Regional Operational Programme and the European Regional Development Fund (ERDF). Additional funding came from Fundação para a Ciência e Tecnologia (Portugal) and the European Research Council (ERC-2013-StG-337747 “C.o.C.O.”). Individual fellowships included support to AP (SFRH/BD/33943/2009). The funders did not influence study design, data collection and analysis, publication decisions, or manuscript preparation.
Original research article (open access): “Thalamic, cortical, and amygdala involvement in the processing of a natural sound cue of danger” by Pereira AG, Farias M, Moita MA. PLOS Biology. DOI: 10.1371/journal.pbio.3000674.
Abstract
Thalamic, cortical, and amygdala involvement in the processing of a natural sound cue of danger
Animals commonly use the auditory consequences of others’ defensive actions to detect threats. This study identifies a neural circuit in rats that detects one such cue: the cessation of movement-generated sounds that accompanies freezing. The circuit includes the dorsal subnucleus of the medial geniculate body (MGD), the ventral area of the auditory cortex (VA), and the lateral amygdala (LA). Together, these findings implicate the auditory offset pathway in processing a natural acoustic cue of danger and demonstrate how sensory and emotional brain regions interact to produce adaptive defensive behavior.
Media contacts: Marta Moita – PLOS
Image source: The image is in the public domain.
Note: This summary distills published findings on neural circuits that link auditory perception—particularly detection of silence—with defensive freezing in rats, as reported in PLOS Biology.
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