Ancient Brainstem Neurons That Help The Brain Ignore Distractions

By Pooja Toshniwal PahariaReviewed by Lauren HardakerJul 2 2026

By uncovering a previously unknown brainstem circuit that filters distractions without disrupting vision or movement, researchers reveal an evolutionarily conserved mechanism that helps the brain select the most important information in complex environments.

Study: Evolutionarily old brainstem neurons are required for the control of selective spatial attention. Image credit: ijoooo/Shutterstock.com

A recent study published in Nature Communications indicates that an evolutionarily old group of brainstem inhibitory neurons, referred to as PLTi, is crucial for guiding attention toward relevant locations in space. The findings could improve understanding of spatially selective information processing for behavioral guidance in healthy and disrupted states and may ultimately help inform research into neuroatypical conditions.

How The Brain Filters Important Information From Distractions

Every moment, the brain is bombarded with information competing for attention. To navigate complex environments successfully, animals must distinguish behaviorally relevant cues from distracting stimuli, allowing them to focus on what matters most for survival. This process depends on both the physical prominence of an object and its relevance to the animal's goals.

Although cortical and fronto-parietal networks are known to support selective attention in mammals, exactly how the brain identifies important targets while suppressing distractions remains unclear. This question is particularly intriguing in vertebrates with less developed cortical structures, prompting researchers to investigate whether evolutionarily ancient brain regions contribute to this fundamental ability. 

Mouse Experiments Revealed How PLTi Shapes Attention

Researchers investigated whether ancient brain regions, including the superior colliculus (SC), contribute to the processing of sensory information and the guidance of behavior. They tested this possibility by training freely moving mice in a behavioral task designed to assess spatial attention.

The team collected midbrain tissue and used gamma-aminobutyric acid (GABA) immunostaining to detect inhibitory neurons within the parabigemino-tegmental complex. They also injected fluorescent tracers and AAV vectors into parvalbumin-positive (PV+) cells to assess SC projections.

The researchers trained freely moving mice on a touchscreen-based flanker task, in which they identified the orientation of a central visual stimulus while ignoring a second peripheral stimulus. The peripheral stimulus was either absent or presented in a matching or opposing orientation. In separate experiments using head-fixed mice, the researchers performed chemogenetic and electrophysiological analyses to investigate the neural mechanisms underlying PLTi function.

The team next investigated whether PLTi is necessary for selective target processing in space. They administered an inhibitory chemogenetic receptor to silence PV+ PLTi on both sides of the brain in freely moving mice. They then investigated whether PLTi is involved in visual perception and movement planning.

The researchers trained the mice on a single-target discrimination task with varying target contrasts. They also compared response rates for the upper and lower ports to assess the potential role of PLTi in movement planning. They also assessed movement orientation by tracking head trajectories and reaction times (RTs).

The team performed drift diffusion modeling (DDM) of RT distributions to investigate how bilateral PLTi silencing altered reaction times. To examine the neural effects of PLTi silencing, they measured stimulus-evoked activity in SCid neurons using electrophysiological recordings from awake, head-fixed mice.

The researchers also examined how PLTi influenced target selection when competing stimuli differed in behavioral importance. They investigated how silencing PLTi altered the point at which mice switched their preference from one stimulus to another, providing insight into how this brain region shapes decision-making. They measured SCid neuronal responses to competing stimuli presented within and outside the neuron's spatial receptive field. They next examined whether silencing PLTi on both sides of the SCid affected competitive interactions within SCid.

PLTi Enables Target Selection Without Affecting Vision

When mice completed a task designed to mimic human spatial attention, silencing PLTi bilaterally impaired their ability to identify the correct target without affecting single-target vision or movement-related task performance. PLTi silencing left intact visual perception, movement planning, and timing of head-orienting responses. Instead, PLTi silencing impaired the ability to distinguish relevant targets from distractors and altered how SCid neurons differentiated between stronger and weaker stimuli.

In the mouse midbrain, PLTi is formed by PV+ inhibitory neurons that project to the SCid and modulate its activity. The study showed that PLTi helps distinguish relevant targets from distractors by regulating competition between their neural representations, without affecting the perception of isolated targets.

PLTi controlled competing stimulus representations in the SC. PLTi altered neural representations of competing stimuli in the SC. The results indicate that this brainstem region may have an evolutionarily conserved role in selecting the most behaviorally relevant target. The results suggest that PLTi plays a role in how SCid resolves competing inputs, guiding attention toward relevant targets.

While PLTi inactivation led to faster (lower) median RTs across task conditions, accuracy declined only during incongruent trials and remained unchanged during single-target and congruent trials. PLTi silencing reduced the DDM threshold, consistent with a lower decision threshold for initiating responses, and was associated with a nonspecific increase in SCid neuronal firing rates in response to single stimuli. The researchers concluded that this increase likely contributed to faster reaction times across task conditions.

Ancient Brainstem Circuit Plays A Key Attention Role

The findings indicate that PLTi helps the brain prioritize important targets by suppressing competing distractions. This points to an important role for this brain region in attention control and identifies PLTi as a specialized brainstem circuit involved in spatial target selection in mice.

In future studies, researchers should investigate the structural and functional changes in mammalian PLTi circuits and explore how the brainstem, thalamic, and fronto-parietal circuits work together to drive spatial target selection among distractors. The authors note that understanding these interactions will be important for explaining both normal spatial attention and the disruptions observed in neuroatypical conditions.

Journal Reference

Kothari, N.B., Banerjee, A., Zhang, Q. et al. (2026). Evolutionarily old brainstem neurons are required for the control of selective spatial attention. Nature Communications, DOI: 10.1038/s41467-026-72340-9. https://link.springer.com/article/10.1038/s41467-026-72340-9