The brain does not need its sophisticated cortex to interpret the visual world. A new study published in PLOS Biology demonstrates that a much older structure, the superior colliculus, contains the necessary circuitry to perform the fundamental computations that allow us to distinguish objects from the background and detect which stimuli are relevant in space. This work reveals that these ancestral circuits, present in the brains of all vertebrates, can generate center–surround interactions independently: a key visual principle that enables the brain to detect contrasts, edges, and salient features in the environment.
“For decades it was thought that these computations were exclusive to the visual cortex, but we have shown that the superior colliculus, a much older structure in evolutionary terms, can also perform them autonomously,” explains Andreas Kardamakis, head of the Neural Circuits in Vision for Action laboratory at the Institute for Neurosciences (IN), a joint centre of the Spanish National Research Council (CSIC) and the Miguel Hernández University (UMH) of Elche, and principal investigator of the study. “This means that the ability to analyse what we see and decide what deserves our attention is not a recent invention of the human brain, but a mechanism that appeared more than half a billion years ago.”
A “radar” in the brain that prioritises what matters
The superior colliculus acts as a kind of biological radar, receiving direct input from the retina and, before information reaches the cerebral cortex, in order to determine which stimuli in the environment are most relevant. When something moves, shines, or suddenly appears in the visual field, this structure is the first to respond and to direct the gaze towards that point.
The study combines several cutting-edge experimental techniques, including patterned optogenetics, electrophysiology, and computational modelling, to investigate how neurons are organised and communicate within the superior colliculus. By using light to activate specific retinal projections in the colliculus and record responses in mouse brain slices, the team observed that the superior colliculus can generate a suppression of the central stimulus when the surrounding area is activated, a hallmark pattern of centre–surround interactions and a mechanism backed by cell-type-specific transynaptic mapping and large-scale modelling.
“We have seen that the superior colliculus not only transmits visual information but also processes and filters it actively, reducing the response to uniform stimuli and enhancing contrasts,” says Kuisong Song, co-first author of the paper. “This demonstrates that the ability to select or prioritise visual information is embedded in the oldest subcortical circuits of the brain.” The results suggest that the function of highlighting what captures our attention does not depend solely on higher cortical areas but is deeply rooted in mechanisms common to all vertebrates.
Evolutionary and cognitive implications
These findings challenge the classical view that complex visual operations are the exclusive domain of the cortex. Instead, they point to a more distributed and hierarchical organisation of the brain, where ancient structures not only relay information but also carry out essential computations for survival, such as detecting predators, tracking prey, or avoiding obstacles.
“Understanding how these ancestral structures contribute to visual attention also helps us understand what happens when these mechanisms fail,” Kardamakis notes. “Disorders such as attention deficit, sensory hypersensitivity, or some forms of traumatic brain injury may partly originate from imbalances between cortical communication and these fundamental circuits”.
His team is now extending these findings to in vivo models to investigate how the superior colliculus shapes visual attention and regulates distractions during goal-directed behavior. Understanding how visual distractors are transformed into behavioral responses is essential for revealing underlying pathophysiological mechanisms, particularly in an era increasingly driven by visual technology.
This study is the result of a broad international collaboration involving the Karolinska Institutet, the KTH Royal Institute of Technology (both in Sweden), and the Massachusetts Institute of Technology (MIT, USA). It also includes the participation of Teresa Femenía, researcher at the IN CSIC-UMH, who made a key contribution to the experimental development of the study.
A shared evolutionary framework for visual attention
In line with this work, Andreas Kardamakis and Giovanni Usseglio have recently published a chapter in the new volume of the Evolution of Nervous Systems series, edited by JH Kass (now appearing in Elsevier, 2025), which expands the comparative and evolutionary perspective of these subcortical visual circuits. In this chapter, the authors review how structures homologous to the superior colliculus, found in fish, amphibians, reptiles, birds, and mammals, share a common functional principle: the integration of sensory and motor information to orient attention and gaze.
The chapter highlights that this brain architecture, preserved for over 500 million years of evolution, forms the common foundation upon which the cortex later developed its higher cognitive functions. “Evolution did not replace these ancient systems; it built upon them,” says Kardamakis, and adds: “We still rely on the same basic hardware to decide where to look and what to ignore.”
This research was supported by Spain’s State Research Agency - Spanish Ministry of Science, Innovation and Universities, the Severo Ochoa Programme for Centres of Excellence, the Generalitat Valenciana through the CIDEGENT programme, the Swedish Research Council, the Swedish Brain Foundation, and the Olle Engkvist Foundation.
Source: Institute for Neurociencias CSIC-UMH (in.comunicacion@umh.es)