Our perception of the world hinges on a delicate balance between the sensory stimuli we receive and the internally generated states of our brain. Yet, how these two forces interact at the neural level—or even where within the brain this complex dialogue plays out—has remained a profound mystery. A groundbreaking study published in Nature Neuroscience in 2026 now sheds new light on this enigmatic process by exploring the activity of single neurons within the primary visual cortex (V1) in macaque monkeys engaged in a visual detection task. This research unravels how fluctuating internal states dynamically modulate neural signals in V1, ultimately influencing behavior.
The primary visual cortex, located at the back of the brain, has conventionally been considered a sensory area that passively processes incoming visual information. However, this study challenges that long-standing notion by demonstrating that the membrane potential—a fundamental electrical property of neurons—in V1 cells exhibits gradual changes well before the visual target even appears. These anticipatory changes suggest an active preparatory mechanism rather than pure stimulus-driven responses.
Researchers employed sophisticated electrophysiological techniques to record the membrane potential (V_m) of individual V1 neurons in macaque monkeys performing a reaction-time task. The animals were trained to respond to visual targets varying in location and contrast, allowing the scientists to capture a rich dataset linking neural dynamics to behavioral outcomes. The membrane potential, as measured, provides a direct window into the excitability and integrative state of single neurons.
One of the most remarkable findings of this research was the observation of a slow depolarization—a gradual increase in membrane potential—that ramped up in anticipation of the target’s onset. Contrary to traditional views focusing only on evoked responses after stimulus presentation, this preparatory depolarization indicates that internal brain states modulate sensory areas in a time-dependent manner, setting the stage for upcoming perception and action.
The study carefully quantified the relationship between these pre-stimulus depolarizations and the monkeys’ reaction times. Intriguingly, trials where neurons exhibited a stronger buildup in membrane potential corresponded to faster behavioral responses, linking internal neural dynamics to perceptual performance. This finding underscores the idea that the brain’s spontaneous fluctuations are not mere noise but functional modulations that shape what we perceive and how quickly we react.
Not only did the researchers find correlations prior to stimulus onset, but post-stimulus membrane potential fluctuations were also strongly tied to the animals’ choices. The neural depolarizations after target presentation varied systematically with the monkey’s visual detection decisions, emphasizing the role of V1 neurons not just in encoding sensory inputs but also in reflecting internal states related to decision-making processes.
Furthermore, these choice-related covariations depended critically on the spatial location and contrast of the visual targets. This spatial and contrast specificity hints at a sophisticated interaction between bottom-up sensory information and top-down internal states, revealing a context-dependent modulation of sensory processing. Essentially, the internal state influences neuronal activity in a way that is finely tuned to the visual scene’s attributes.
To interpret these complex observations, the team devised a computational model incorporating fluctuating multiplicative gain—a mechanism by which the internal state multiplicatively scales neural responses. This model could recapitulate both the preparatory depolarizations and the choice-related fluctuations, providing a unifying framework that bridges cellular electrophysiology with behavioral outcomes.
The fluctuating multiplicative gain model suggests that nonlinear modulations of synaptic input or intrinsic cellular excitability occur at or even before the level of V1. This challenges the classical feedforward view of sensory processing, arguing for a more interactive and dynamic system where internal brain states actively shape early sensory representations.
These findings have far-reaching implications for understanding perception and cognition. By framing sensory cortex activity as a dynamic interplay between external stimuli and internally driven modulatory states, the study prompts a reevaluation of how the brain integrates information to guide behavior. It also propels forward the idea that variability in neural responses, far from being mere noise, carries meaningful signals related to internal cognitive states.
The results also invite consideration of how internal states such as attention, expectation, and arousal manifest at the neural circuit level. The slow buildup of membrane potential preceding targets could reflect attentional anticipation or preparatory readiness, linking cellular physiology with higher-order cognitive functions.
Moreover, the dependence of neural-behavioral correlations on stimulus contrast and location indicates that internal states do not act uniformly but rather interact with sensory inputs in a highly structured manner. This layered modulation could underpin the brain’s remarkable flexibility in adapting perception based on context and prior knowledge.
The experimental approach, combining intracellular recordings with behavioral measurements in nonhuman primates, represents a powerful methodology to dissect the neural correlates of perception. It bridges the gap between single-cell electrophysiology and complex behaviors, offering a precise lens into the computations carried out by the visual cortex during real-time tasks.
Overall, this landmark study reframes our understanding of visual processing as a dynamically modulated signal, shaped not only by the world outside but crucially by the brain’s internal milieu. The membrane potential of V1 neurons provides a tangible neurophysiological substrate for internal states influencing perception and reaction, illustrating how deeply intertwined our experience of the world is with the brain’s ongoing internal dynamics.
Looking ahead, these insights could have profound consequences for developing treatments targeting perceptual disorders or attentional deficits. By deciphering how internal states modulate sensory cortex function, neuroscientists can better understand pathological conditions where this interplay is disrupted, such as schizophrenia or attention deficit disorders.
This work also opens avenues for novel brain-computer interfaces and neuroprosthetics that tap into the brain’s internal state fluctuations to enhance sensory perception and behavior. By harnessing the intrinsic dynamics of neural circuits, future technologies may achieve more naturalistic and adaptive interactions aligned with an individual’s internal state.
In sum, the demonstration that fluctuating internal states mediate neural-behavioral covariations in the primary visual cortex marks a significant advance in sensory neuroscience. It challenges simplistic stimulus-response paradigms and highlights the brain’s intrinsic activity as a key player in shaping our perceptual reality and behavioral choices. This study adds a pivotal chapter to our quest for understanding the brain’s most fundamental mechanisms.
Subject of Research: Neural mechanisms underlying the interaction between internal brain states and sensory processing in the primary visual cortex (V1) during visual perception.
Article Title: Fluctuating internal states mediate neural–behavioral covariations in V1
Article References:
Li, B., Samonds, J.M., Chen, Y. et al. Fluctuating internal states mediate neural–behavioral covariations in V1. Nat Neurosci (2026). https://doi.org/10.1038/s41593-026-02296-y
Image Credits: AI Generated
