Intracortical Inhibition Assessed with Paired-Pulse Transcranial Magnetic Stimulation is Modulated during Shortening and Lengthening Contractions in Young and Old Adults

• Main Authors: George M. Opie, John G. Semmler
• Format: Article
• Language: English
• Published: Elsevier 2016-03-01
• Series: Brain Stimulation
• Subjects: Transcranial magnetic stimulation; Gamma aminobutyric acid; Ageing; Anisometric contractions
• Online Access: http://www.sciencedirect.com/science/article/pii/S1935861X15012577

Background: The modulation of intracortical inhibition is thought to be impaired in older adults, which may contribute to their reduced fine motor control, particularly during lengthening muscle contractions. Objective: To quantify the magnitude of intracortical inhibition and movement performance during postural, shortening and lengthening contractions of a hand muscle in young and old adults. Methods: In 18 young (23.2 ± 4.2) and 16 old (70.6 ± 6.5) subjects, paired-pulse transcranial magnetic stimulation (TMS) was used to assess short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) during a movement task involving the first dorsal interosseous muscle. The task required a constant load (50 g) to be slowly lifted and lowered using the index finger while single- or paired-pulse TMS was delivered during the shortening or lengthening contraction. Results: Relative to postural contractions, SICI during shortening contractions was reduced by 29% in young subjects (P < 0.0001) and 43% in old subjects (P < 0.0001), whereas SICI during lengthening contractions was reduced by 11% in young subjects (P = 0.0004) and 33% in old subjects (P < 0.0001). Furthermore, SICI was significantly less in older adults during lengthening contractions (P-values < 0.01). For LICI, inhibition was not influenced by contraction type in old subjects, but was increased by 11% during shortening contractions (P < 0.0001) and by 9% during lengthening contractions in young subjects (P = 0.0008). In addition, old subjects showed significantly less LICI than young subjects in each movement phase (both P-values < 0.05). Conclusions: Shortening and lengthening contractions with a constant load are associated with a modulation of GABAergic inhibition that is altered by healthy ageing.