Vesia Michael, Barnett-Cowan Michael, Elahi Behzad, Jegatheeswaran Gaayathiri, Isayama Reina, Neva Jason L, Davare Marco, Staines W Richard, Culham Jody C, Chen Robert
Krembil Research Institute, University Health Network and Division of Neurology, University of Toronto, Toronto, ON, Canada.
Department of Psychology, Brain and Mind Institute, University of Western Ontario, London, ON, Canada; Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada.
Cortex. 2017 Jul;92:175-186. doi: 10.1016/j.cortex.2017.04.007. Epub 2017 Apr 19.
According to one influential view, two specialized parieto-frontal circuits control prehension: a dorsomedial stream for hand transport during reaching and a dorsolateral stream for preshaping the fingers during grasping. However, recent evidence argues that an area within the dorsomedial stream-macaque area V6A and, its putative human homolog, superior parietal occipital cortex (SPOC) - encodes both hand transport and grip formation. We tested whether planning varied hand actions modulates functional connectivity between left SPOC and ipsilateral primary motor cortex (M1) using a dual-site, paired-pulse transcranial magnetic stimulation paradigm with two coils (TMS). Participants performed three different hand actions to a target object comprising a small cylinder atop a larger cylinder. These actions were: reaching-to-grasp the top (GT) using a precision grip, reaching-to-grasp the bottom (GB) using a whole-hand grip, or reaching-to-touch (Touch) the side of the target object without forming a grip. Motor-evoked potentials (MEPs) from TMS to M1, with or without preceding TMS to SPOC, were recorded from first dorsal interosseous (FDI) and abductor digiti minimi (ADM) hand muscles in two experiments that varied timing parameters (the stimulus onset asynchrony, SOA, between the 'GO' cue and stimulation and interpulse interval, IPI, between SPOC and M1 stimulation). We found that preparatory response amplitudes in the SPOC-M1 circuit of different hand muscles were selectively modulated early in the motor plan for different types of grasps. First, based on SPOC-M1 interactions, across two experiments, the role of the ADM was facilitated during a whole-hand grasp of a large object (GB) relative to other conditions under certain timing parameters (SOA = 150 msec; IPI = 6 msec). Second, the role of the FDI was facilitated during hand action planning compared to rest. These findings suggest that the human dorsomedial parieto-motor stream plays a causal role in planning grip formation for object-directed actions.
根据一种有影响力的观点，两个特定的顶叶 - 额叶回路控制抓握动作：一个是背内侧通路，用于在伸手时手部的移动；另一个是背外侧通路，用于在抓握时对手指进行预塑形。然而，最近的证据表明，背内侧通路中的一个区域——猕猴的V6A区及其假定的人类同源区域，即顶上枕叶皮质（SPOC）——对手部移动和抓握动作的形成都进行编码。我们使用双部位、双线圈经颅磁刺激（TMS）范式，测试了计划不同手部动作是否会调节左侧SPOC与同侧初级运动皮层（M1）之间的功能连接。参与者对一个由位于较大圆柱体顶部的小圆柱体组成的目标物体执行三种不同的手部动作。这些动作分别是：使用精确抓握方式伸手去抓顶部（GT）、使用全手握抓方式伸手去抓底部（GB），或者伸手去触摸（Touch）目标物体的侧面而不形成抓握动作。在两个改变时间参数（“开始”提示与刺激之间的刺激起始异步时间，SOA，以及SPOC和M1刺激之间的脉冲间隔，IPI）的实验中，记录了从TMS到M1的运动诱发电位（MEP），无论之前是否有对SPOC的TMS刺激，均记录自第一骨间背侧肌（FDI）和小指展肌（ADM）手部肌肉。我们发现，在针对不同类型抓握的运动计划早期，不同手部肌肉的SPOC - M1回路中的准备反应幅度会受到选择性调节。首先，基于SPOC - M1的相互作用，在两个实验中，在特定时间参数（SOA = 150毫秒；IPI = 6毫秒）下，相对于其他条件，在全手握抓大物体（GB）时，ADM的作用得到了增强。其次，与休息时相比，在手部动作计划期间，FDI的作用得到了增强。这些发现表明，人类背内侧顶叶 - 运动通路在为目标导向动作计划抓握动作的形成过程中起到了因果作用。
