Direct cortical stimulation induces short-term plasticity of neural oscillations in humans.

Patterned brain stimulation is commonly employed as a tool for eliciting plasticity in brain circuits and treating neuropsychiatric disorders. Although widely used in clinical settings, there remains a limited understanding of how stimulation-induced plasticity influences neural oscillations and their interplay with the underlying baseline functional architecture. To address this question, we applied 15 minutes of 10Hz focal electrical simulation, a pattern identical to 'excitatory' repetitive transcranial magnetic stimulation (rTMS), to 14 medically-intractable epilepsy patients undergoing intracranial electroencephalographic (iEEG). We quantified the spectral features of the cortico-cortical evoked potential (CCEPs) in these patients before and after stimulation. We hypothesized that for a given region the temporal and spectral components of the CCEP predicted the location and degree of stimulation-induced plasticity. Across patients, low frequency power (alpha and beta) showed the broadest change, while the magnitude of change was stronger in high frequencies (beta and gamma). Next we demonstrated that regions with stronger baseline evoked spectral responses were more likely to undergo plasticity after stimulation. These findings were specific to a given frequency in a specific temporal window. Post-stimulation power changes were driven by the interaction between direction of change in baseline power and temporal window of change. Finally, regions exhibiting early increases and late decreases in evoked baseline power exhibited power changes after stimulation and were independent of stimulation location. Together, these findings that time-frequency baseline features predict post-stimulation plasticity effects demonstrate properties akin to Hebbian learning in humans and extend this theory to the temporal and spectral window of interest. These findings can help improve our understanding of human brain plasticity and lead to more effective brain stimulation techniques.

Personalized Repetitive Transcranial Magnetic Stimulation for Depression.

Personalized treatments are gaining momentum across all fields of medicine. Precision medicine can be applied to neuromodulatory techniques, in which focused brain stimulation treatments such as repetitive transcranial magnetic stimulation (rTMS) modulate brain circuits and alleviate clinical symptoms. rTMS is well tolerated and clinically effective for treatment-resistant depression and other neuropsychiatric disorders. Despite its wide stimulation parameter space (location, angle, pattern, frequency, and intensity can be adjusted), rTMS is currently applied in a one-size-fits-all manner, potentially contributing to its suboptimal clinical response (∼50%). In this review, we examine components of rTMS that can be optimized to account for interindividual variability in neural function and anatomy. We discuss current treatment options for treatment-resistant depression, the neural mechanisms thought to underlie treatment, targeting strategies, stimulation parameter selection, and adaptive closed-loop treatment. We conclude that a better understanding of the wide and modifiable parameter space of rTMS will greatly improve the clinical outcome.

Gastrocnemius Medial Head Stiffness Is Associated with Potential Fall Risk in Community-Dwelling Older Adults.

The aim of this study is to compare the muscle strength, balance ability, thickness, and stiffness of the tibialis anterior and gastrocnemius muscle in the elderly, with (fallers) and without (non-fallers) fall experience, and confirmed the correlation between the variables mentioned above and muscle stiffness in the faller. We selected 122 elderly participants, comprising 40 fallers and 82 non-fallers, and measured the muscle strength of the tibialis anterior (TA) and the gastrocnemius (GA). Balance ability was measured by the functional reach test (FRT), timed up and go test (TUG), short physical performance battery (SPPB), and gait speed (GS). We used shear wave elastography (SWE) to determine the thickness of the TA and the medial (GAmed) and lateral head (GAlat) of the gastrocnemius and the stiffness during relaxation and contraction. Balance ability, except muscle strength, was significantly lower in fallers compared with non-fallers. The GAmed and GAlat thickness were significantly lower in fallers than that in non-fallers. In fallers, the thickness, rest, and contractive stiffness of GAmed were correlated with the FRT, GS, SPPB. Low rest and GAmed contractive stiffness were related to lower balance ability in fallers. The muscle stiffness measurement using SWE was a novel method to assess potential fall risk.