Why does looking at groups of neurons change the story?
Most early studies of adaptation focused on single neurons: a repeated stimulus makes one neuron respond less. But perception depends on the combined activity of many neurons, and adaptation can change the pattern across the population even when individual responses are suppressed. A review of visual cortex adaptation argues that the field needs to move beyond single-neuron studies to understand how population-level adaptation relates to perception [1].
In the cerebellum, recordings during a sensorimotor adaptation task show that complex spikes across many Purkinje cells become synchronized in a way that reflects behavioral adaptation. This population-level modulation is not just a sum of individual changes; it suggests that adaptation can coordinate activity across cells to support learning and adjustment [3].
How do population changes alter what we perceive?
When adaptation alters the responses of a population of neurons, it can shift the neural representation of a stimulus. For example, if some neurons reduce their response more than others, the overall pattern of activity across the population may change, potentially making a stimulus appear different or altering its perceived intensity. The visual cortex review emphasizes that population-level adaptation is likely tied to perceptual aftereffects, though the precise link is still an open question [1].
In touch, computational modeling of tactile afferents suggests that perception depends on population-level signals, not just single afferent responses. The model predicts how active touch shapes neural dynamics across a population, which could explain how adaptation during active exploration influences what we feel [2].
When does adaptation do more than just suppress?
Adaptation can also involve changes in the timing or synchronization of spikes across neurons, as seen in the cerebellum during behavioral adaptation. There, complex spikes across Purkinje cells modulate together, which may help the brain anticipate or correct for errors. This goes beyond simple suppression: it's a population-level reorganization that supports learning [3].
The visual cortex review notes that natural stimuli, which activate diverse populations of neurons, are particularly useful for studying adaptation because they engage the population in a more realistic way. Such studies could reveal how adaptation shapes the population code under conditions closer to everyday perception [1].
Sources used in this answer
Adaptation in the visual cortex: a case for probing neuronal populations with natural stimuli
The review argues that adaptation research should shift from single-neuron studies to population-level analyses using natural stimuli to better understand perception.
From skin mechanics to tactile neural coding: Predicting afferent neural dynamics during active touch and perception
A computational model predicts tactile neural dynamics and suggests perception depends on population-level afferent signals during active touch.
Population-level modulation of Purkinje cell complex spikes during behavioural adaptation to imposed sensorimotor error
Purkinje cell complex spikes show population-level modulation and synchronization during behavioral adaptation to sensorimotor error.