Dipole Source Analyses of Early Median Nerve SEP Components Obtained From Subdural Grid Recordings

BackgroundThe exact origin of neuronal responses in the human sensorimotor cortex subserving the generation of voluntary movements remains unclear, despite the presence of characteristic but robust waveforms in the records of electroencephalography or magnetoencephalography (MEG).AimsTo clarify this fundamental and important problem, we analyzed MEG in more detail using a multidipole model during pulsatile extension of the index finger, and made some important new findings.ResultsMovement-related cerebral fields (MRCFs) were confirmed over the sensorimotor region contralateral to the movement, consisting of a temporal succession of the first premovement component termed motor field, followed by two or three postmovement components termed movement evoked fields. A source analysis was applied to separately model each of these field components. Equivalent current diploes of all components of MRCFs were estimated to be located in the same precentral motor region, and did not differ with respect to their locations and orientations. The somatosensory evoked fields following median nerve stimulation were used to validate these findings through comparisons of the location and orientation of composite sources with those specified in MRCFs. The sources for the earliest components were evoked in Brodmann's area 3b located lateral to the sources of MRCFs, and those for subsequent components in area 5 and the secondary somatosensory area were located posterior to and inferior to the sources of MRCFs, respectively. Another component peaking at a comparable latency with the area 3b source was identified in the precentral motor region where all sources of MRCFs were located.ConclusionThese results suggest that the MRCF waveform reflects a series of responses originating in the precentral motor area.

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“…; see also Baumgärtner et al. ), whereas Jung et al. () localized the P22 dipole source in area 4, using an EEG dipole source analysis.…”

Section: Discussionmentioning

confidence: 99%

Reappraisal of field dynamics of motor cortex during self‐paced finger movements

et al. 2013

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“…In addition, as highlighted above, while it has been proposed that the P22 SEP component may originate from the precentral motor area, the balance of evidence now indicates that the source is in area 1 (i.e., S1) (Baumgartner et al, 2010). It is also worth noting in this context that while S1 areas 1, 2 and are represented across the ventrobasal complex of the thalamus, area 3a has connectional relationships similar to those for area 4 (Jones et al, 1979), further emphasizing the likelihood that muscle afferent input relayed via area 3a will have a more direct influence on the state of the primary motor cortex, than cutaneous input relayed via other regions of S1.…”

Section: Mediation Of Interactions Between the Constituent Elements Omentioning

confidence: 99%

Modulation of human corticospinal excitability by paired associative stimulation

Carson

Kennedy

2013

Front. Hum. Neurosci.

126

141

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Paired Associative Stimulation (PAS) has come to prominence as a potential therapeutic intervention for the treatment of brain injury/disease, and as an experimental method with which to investigate Hebbian principles of neural plasticity in humans. Prototypically, a single electrical stimulus is directed to a peripheral nerve in advance of transcranial magnetic stimulation (TMS) delivered to the contralateral primary motor cortex (M1). Repeated pairing of the stimuli (i.e., association) over an extended period may increase or decrease the excitability of corticospinal projections from M1, in manner that depends on the interstimulus interval (ISI). It has been suggested that these effects represent a form of associative long-term potentiation (LTP) and depression (LTD) that bears resemblance to spike-timing dependent plasticity (STDP) as it has been elaborated in animal models. With a large body of empirical evidence having emerged since the cardinal features of PAS were first described, and in light of the variations from the original protocols that have been implemented, it is opportune to consider whether the phenomenology of PAS remains consistent with the characteristic features that were initially disclosed. This assessment necessarily has bearing upon interpretation of the effects of PAS in relation to the specific cellular pathways that are putatively engaged, including those that adhere to the rules of STDP. The balance of evidence suggests that the mechanisms that contribute to the LTP- and LTD-type responses to PAS differ depending on the precise nature of the induction protocol that is used. In addition to emphasizing the requirement for additional explanatory models, in the present analysis we highlight the key features of the PAS phenomenology that require interpretation.

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“…SEPs and SEFs were not precisely matched in latency, as expected, because MEG is insensitive to radially oriented sources while SEP components are supposedly, generated, in part, by radially oriented sources ( Baumgärtner et al, 2010 ). The discrepancy does not reduce the significance of our main finding, showing that, in CM, SEPs become giant only after the first cortical potential.…”

Section: Discussionmentioning

confidence: 74%

Giant early components of somatosensory evoked potentials to tibial nerve stimulation in cortical myoclonus

Anzellotti

Onofrj

Bonanni

et al. 2016

NeuroImage: Clinical

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Enlarged cortical components of somatosensory evoked potentials (giant SEPs) recorded by electroencephalography (EEG) and abnormal somatosensory evoked magnetic fields (SEFs) recorded by magnetoencephalography (MEG) are observed in the majority of patients with cortical myoclonus (CM). Studies on simultaneous recordings of SEPs and SEFs showed that generator mechanism of giant SEPs involves both primary sensory and motor cortices. However the generator sources of giant SEPs have not been fully understood as only one report describes clearly giant SEPs following lower limb stimulation. In our study we performed a combined EEG-MEG recording on responses elicited by electric median and tibial nerve stimulation in a patient who developed consequently to methyl bromide intoxication CM with giant SEPs to median and tibial nerve stimuli.SEPs wave shapes were identified on the basis of polarity-latency components (e.g. P15-N20-P25) as defined by earlier studies and guidelines. At EEG recording, the SEP giant component did not appear in the latency range of the first cortical component for median nerve SEP (N20), but appeared instead in the range of the P37 tibial nerve SEP, which is currently identified as the first cortical component elicited by tibial nerve stimuli. Our MEG and EEG SEPs recordings also showed that components in the latency range of P37 were preceded by other cortical components. These findings suggest that lower limb P37 does not correspond to upper limb N20. MEG results confirmed that giant SEFs are the second component from both tibial (N43m-P43m) and median (N27m-P27m) nerve stimulation. MEG dipolar sources of these giant components were located in the primary sensory and motor area.

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Dipole Source Analyses of Early Median Nerve SEP Components Obtained From Subdural Grid Recordings

Cited by 18 publications

References 73 publications

Reappraisal of field dynamics of motor cortex during self‐paced finger movements

Reappraisal of field dynamics of motor cortex during self‐paced finger movements

Modulation of human corticospinal excitability by paired associative stimulation

Giant early components of somatosensory evoked potentials to tibial nerve stimulation in cortical myoclonus

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