Area 5 Influences Excitability within the Primary Motor Cortex in Humans

Abstract

In non-human primates, Brodmann's area 5 (BA 5) has direct connectivity with primary motor cortex (M1), is largely dedicated to the representation of the hand and may have evolved with the ability to perform skilled hand movement. Less is known about human BA 5 and its interaction with M1 neural circuits related to hand control. The present study examines the influence of BA 5 on excitatory and inhibitory neural circuitry within M1 bilaterally before and after continuous (cTBS), intermittent (iTBS), and sham theta-burst stimulation (sham TBS) over left hemisphere BA 5. Using single and paired-pulse TMS, measurements of motor evoked potentials (MEPs), short interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were quantified for the representation of the first dorsal interosseous muscle. Results indicate that cTBS over BA 5 influences M1 excitability such that MEP amplitudes are increased bilaterally for up to one hour. ITBS over BA 5 results in an increase in MEP amplitude contralateral to stimulation with a delayed onset that persists up to one hour. SICI and ICF were unaltered following TBS over BA 5. Similarly, F-wave amplitude and latency were unaltered following cTBS over BA 5. The data suggest that BA 5 alters M1 output directed to the hand by influencing corticospinal neurons and not interneurons that mediate SICI or ICF circuitry. Targeting BA 5 via cTBS and iTBS is a novel mechanism to powerfully modulate activity within M1 and may provide an avenue for investigating hand control in healthy populations and modifying impaired hand function in clinical populations.

Neural effects of short-term training on working memory

“…BA 6 and BA 39 are regions that are often associated with aspects of executive control (Wager & Smith, 2003), and we found increases in perfusion in both of these regions. Contrary to our expectations, we found a reduction in perfusion at rest in right BA 5, which is part of association cortex and often associated with finger and hand movements (Premji, Rai, & Nelson, 2011). Nonetheless, activation changes in this region have also been observed as a function of n back training (Schneiders et al, 2012).…”

A Review of Transcranial Magnetic Stimulation and Multimodal Neuroimaging to Characterize Post-Stroke Neuroplasticity

“…Importantly, the specific effects of cTBS and iTBS show substantial inter-individual variability, which likely depends upon which interneuron populations are activated by the TMS pulse ( 196 ). rTMS protocols, like TBS, have been shown to modulate cortical excitability, and at times behavior, when applied over motor-related areas, such as M1 ( 190 ), contralateral M1 ( 197 , 198 ), the SMA ( 199 ), the dorsal premotor cortex (PMd) ( 200 ), the primary somatosensory cortex (S1) ( 194 ), area 5 ( 201 ), as well as non-motor areas, such as the cerebellum ( 202 ) and the DLPFC ( 203 ). Not only does rTMS modulate cortical activity directly below the magnetic coil, but activity in remote cortical and subcortical regions can be modified by application of rTMS over a single cortical target ( 204 ).…”

Neural correlates of visuomotor adjustments during scaling of human finger movements

“…In non‐human primates, the connection of area 5 to M1 has been described anatomically as well as functionally (Strick & Kim, ; Zarzecki et al ., ). In human it has been shown by transcranial magnetic stimulation studies that BA 5 influences excitability in M1 (Premji et al ., 2010, Premji et al ., ). Diedrichsen et al .…”