We are watching a show after lunch or reading a book on the train ride home and, without realizing it, we begin to lose track. We still hear voices, feel the phone vibrate and perceive what is happening around us. We are entering a state of drowsiness—a gray zone between alert wakefulness and sleep where our connection with the environment begins to fluctuate. On that boundary between consciousness and unconsciousness, is the brain still capable of effectively combining information received through different senses?
In a recent study published in The Journal of Neuroscience and conducted at the Mind, Brain and Behavior Research Center (CIMCYC) at the University of Granada, in collaboration with the University of Cambridge, Clara Alameda, Chiara Avancini, Daniel Sanabria, Tristan A. Bekinschtein and Luis F. Ciria investigated what happens to multisensory integration when alertness declines.
Drowsiness Alters Brain Dynamics, but Preserves the Fundamental Mechanisms of Multisensory Integration
In recent years, various studies have explored which capabilities are maintained and which deteriorate during the transition to sleep. To do so, researchers recreated nap-like situations in the laboratory: participants performed different tasks while being allowed to fall asleep as their brain activity was recorded.
These studies demonstrated that even during drowsiness, the ability to detect stimuli, make simple decisions and even learn new rules is preserved—though responses become slower, errors increase and moments of disconnection emerge. However, these investigations primarily examined the senses in isolation.
Everyday experience, by contrast, is multisensory. The brain continuously combines information from different senses to interpret what occurs in the environment. If a phone vibrates and rings simultaneously, for instance, it is typically detected faster than if it only vibrates or rings. This advantage is known as the "redundancy gain effect," one of the behavioral indicators of multisensory integration.
Traces of this integration can also be observed in the brain. When receiving information through two senses simultaneously, the combined neural response can differ from the simple sum of responses to each sense individually. These differences—which may reflect greater responses ("superadditivity") or reduced ones—indicate that both signals interact during processing.
To examine these phenomena during drowsiness, 26 participants performed a task while reclining with their eyes closed as they progressively fell asleep. They received sounds, light vibrations on their arm or both stimuli simultaneously, and were asked to respond as quickly as possible. Their brain activity was recorded using electroencephalography (EEG), allowing researchers to track their moment-to-moment alertness levels.
During drowsiness, responses were slower and non-response moments increased. However, the benefit of receiving sound and vibration simultaneously remained: participants continued to respond faster to multisensory stimuli.
At the neural level, however, a different story unfolded. Using traditional analyses, the interactions between auditory and tactile information observed during wakefulness appeared later, weakened or ceased to be detectable during drowsiness. Did this mean the brain had stopped integrating both senses? More detailed analyses suggested otherwise: multisensory information maintained a similar structure during both wakefulness and drowsiness, although its activity patterns were less stable over time.
These findings show that drowsiness does not "turn off" the brain's ability to integrate information from different senses. Fundamental operations appear to persist, even as the underlying brain dynamics change.
Reference
Alameda, C., Avancini, C., Sanabria, D., Bekinschtein, T. A., & Ciria, L. F. (2026). Drowsiness alters the neural dynamics but not the core computations of multisensory integration. The Journal of Neuroscience, 46(30), e0363262026. https://doi.org/10.1523/JNEUROSCI.0363-26.2026
Contact
Clara Alameda – clara.alameda@ugr.es