The details of past actions on a smartphone touchscreen are reflected by intrinsic sensorimotor dynamics.

Unconstrained day-to-day activities are difficult to quantify and how the corresponding movements shape the brain remain unclear. Here, we recorded all touchscreen smartphone interactions at a sub-second precision and show that the unconstrained day-to-day behavior captured on the phone reflects in the simple sensorimotor computations measured in the laboratory. The behavioral diversity on the phone, the speed of interactions, the amount of social & non-social interactions, all uniquely influenced the trial-to-trial motor variability used to measure the amount of intrinsic neuronal noise. Surprisingly, both the motor performance and the early somatosensory cortical signals (assessed using EEG in passive conditions) became noisier with increased social interactions. Inter-individual differences in how people use the smartphone can help thus decompose the structure of low-level sensorimotor computations.

Use-dependent cortical processing from fingertips in touchscreen phone users.

Cortical activity allotted to the tactile receptors on fingertips conforms to skilful use of the hand. For instance, in string instrument players, the somatosensory cortical activity in response to touch on the little fingertip is larger than that in control subjects. Such plasticity of the fingertip sensory representation is not limited to extraordinary skills and occurs in monkeys trained to repetitively grasp and release a handle as well. Touchscreen phones also require repetitive finger movements, but whether and how the cortex conforms to this is unknown. By using electroencephalography (EEG), we measured the cortical potentials in response to mechanical touch on the thumb, index, and middle fingertips of touchscreen phone users and nonusers (owning only old-technology mobile phones). Although the thumb interacted predominantly with the screen, the potentials associated with the three fingertips were enhanced in touchscreen users compared to nonusers. Within the touchscreen users, the cortical potentials from the thumb and index fingertips were directly proportional to the intensity of use quantified with built-in battery logs. Remarkably, the thumb tip was sensitive to the day-to-day fluctuations in phone use: the shorter the time elapsed from an episode of intense phone use, the larger the cortical potential associated with it. Our results suggest that repetitive movements on the smooth touchscreen reshaped sensory processing from the hand and that the thumb representation was updated daily depending on its use. We propose that cortical sensory processing in the contemporary brain is continuously shaped by the use of personal digital technology.