Transfer of cognitive training across magnitude dimensions achieved with concurrent brain stimulation of the parietal lobe

Abstract

Improvement in performance following cognitive training is known to be further enhanced when coupled with brain stimulation. Here we ask whether training-induced changes can be maintained long term and, crucially, whether they can extend to other related but untrained skills. We trained overall 40 human participants on a simple and well established paradigm assessing the ability to discriminate numerosity--or the number of items in a set--which is thought to rely on an "approximate number sense" (ANS) associated with parietal lobes. We coupled training with parietal stimulation in the form of transcranial random noise stimulation (tRNS), a noninvasive technique that modulates neural activity. This yielded significantly better and longer lasting improvement (up to 16 weeks post-training) of the precision of the ANS compared with cognitive training in absence of stimulation, stimulation in absence of cognitive training, and cognitive training coupled to stimulation to a control site (motor areas). Critically, only ANS improvement induced by parietal tRNS + Training transferred to proficiency in other parietal lobe-based quantity judgment, i.e., time and space discrimination, but not to quantity-unrelated tasks measuring attention, executive functions, and visual pattern recognition. These results indicate that coupling intensive cognitive training with tRNS to critical brain regions resulted not only in the greatest and longer lasting improvement of numerosity discrimination, but importantly in this enhancement being transferable when trained and untrained abilities are carefully chosen to share common cognitive and neuronal components.

Figure 1.

The training paradigm and the tasks used. A, Participants in the parietal or motor tRNS + Training and in the Training Only groups were trained intensively (560 trials per day) on a numerosity discrimination task for 5 consecutive days, i.e., day 2–6 while (B) receiving real or sham stimulation to the parietal or motor areas. Participants on the Stimulation Only group received no training. Before the training (day 1, pretraining), all participants were tested with (C) the numerosity discrimination task in addition to other continuous quantity-based tasks (time and space discrimination), arithmetic and control tasks. The same cognitive tasks were repeated at the end of the training (day 7, post-training) to test for any training-induced change, and (D) in the parietal tRNS + Training and Training Only groups again at week 4, 8, 12, and 16 post-training to test for any long-term effect of the training.

Figure 2.

Results. Performance in the four groups expressed as Weber fraction in (A) the numerosity discrimination task at pretraining and at post-training, during each of the training days, and at week 4, 8, 12, and 16 after training; in the transfer tasks, i.e., time (B) and space (C) discrimination at pretraining and post-training; and (D) in tasks measuring arithmetic, attention, executive functions, and visual pattern recognition showing no training-induced changes in accuracy (correct answers) or RTs measured as percentage change from pretraining. Smaller wf indicate better performance.