Talelli P, Waddingham W, Ewas A, Rothwell J C, Ward N S
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, Queen SQ, Box 146, London WC1N 3BG, UK.
Exp Brain Res. 2008 Mar;186(1):59-66. doi: 10.1007/s00221-007-1205-8. Epub 2007 Nov 27.
Normal aging is associated with less lateralised task-related activation of the primary motor cortices. It has been hypothesized, but not tested, that this phenomenon is mediated transcallosaly. We have used Transcranial Magnetic Stimulation to look for age-related changes in interhemispheric inhibition (IHI). Thirty healthy individuals (aged 19-78 years) were studied using a paired-pulse protocol at rest and during a low-strength isometric contraction with the right hand. The IHI targeting the right motor cortex was assessed at two intervals, 10 ms (IHI10) and 40 ms (IHI40). The corticospinal excitability of the left hemisphere was assessed by means of input-output curves constructed during voluntary construction. Age was not correlated with IHI10 or IHI40 at rest. During muscle contraction IHI tended to increase at both intervals. However, this increase in IHI during the active condition (changeIHI) was less evident with advancing age for the 40 ms interval (r = 0.444, P = 0.02); in fact a degree of disinhibition was often present. There was no correlation between age and changeIHI10. Age was negatively correlated with the area under the recruitment curve (r = -0.585, P = 0.001) and the size of the maximum MEP collected (r = -0.485, P = 0.007). ChangeIHI and measures of corticospinal excitability were not intercorrelated. In conclusion, task-related increases in interhemispheric inhibition seem to diminish with advancing age. This phenomenon is specific for long-latency IHI and may underlie the age-related bihemispheric activation seen in functional imaging studies. The mechanism underlying changes in IHI with advancing age and the association with changes in corticospinal excitability need further investigation.
正常衰老与初级运动皮层与任务相关的激活较少偏侧化有关。据推测（但未得到验证），这种现象是通过胼胝体介导的。我们使用经颅磁刺激来寻找半球间抑制（IHI）与年龄相关的变化。对30名健康个体（年龄在19 - 78岁之间）进行了研究，采用配对脉冲方案，分别在静息状态和右手进行低强度等长收缩时进行。在两个时间间隔，即10毫秒（IHI10）和40毫秒（IHI40）时评估针对右侧运动皮层的IHI。通过在自主收缩过程中构建输入 - 输出曲线来评估左半球的皮质脊髓兴奋性。年龄与静息时的IHI10或IHI40无关。在肌肉收缩期间，两个时间间隔的IHI都有增加的趋势。然而，对于40毫秒的时间间隔，随着年龄的增长，活动状态下IHI的这种增加（changeIHI）不太明显（r = 0.444，P = 0.02）；实际上，经常会出现一定程度的去抑制。年龄与changeIHI10之间没有相关性。年龄与募集曲线下的面积呈负相关（r = -0.585，P = 0.001）以及收集到 的最大运动诱发电位的大小呈负相关（r = -0.485，P = 0.007）。ChangeIHI与皮质脊髓兴奋性的测量指标之间没有相关性。总之，与任务相关的半球间抑制增加似乎随着年龄的增长而减弱。这种现象是长潜伏期IHI所特有的，可能是功能成像研究中所见的与年龄相关的双侧激活的基础。随着年龄增长IHI变化的潜在机制以及与皮质脊髓兴奋性变化的关联需要进一步研究。
