Models of source currents in the brain

Ilmoniemi, Risto J.

doi:10.1007/bf01128686

Cited by 67 publications

(35 citation statements)

References 24 publications

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“…Further processing was performed by using the MNE Suite 2.6.0 software. Cortical sources of the observed neuromagnetic activity were estimated by using signals from all 306 sensors and L2 MNE approach, which models the recorded magnetic field distribution with the smallest amount of overall source activity (53,54).…”

Section: Methodsmentioning

confidence: 99%

Automatic ultrarapid activation and inhibition of cortical motor systems in spoken word comprehension

Shtyrov

Butorina

Nikolaeva

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

119

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To address the hotly debated question of motor system involvement in language comprehension, we recorded neuromagnetic responses elicited in the human brain by unattended actionrelated spoken verbs and nouns and scrutinized their timecourse and neuroanatomical substrates. We found that already very early on, from ∼80 ms after disambiguation point when the words could be identified from the available acoustic information, both verbs and nouns produced characteristic somatotopic activations in the motor strip, with words related to different body parts activating the corresponding body representations. Strikingly, along with this category-specific activation, we observed suppression of motorcortex activation by competitor words with incompatible semantics, documenting operation of the neurophysiological principles of lateral/surround inhibition in neural word processing. The extremely early onset of these activations and deactivations, their emergence in the absence of attention, and their similar presence for words of different lexical classes strongly suggest automatic involvement of motor-specific circuits in the perception of actionrelated language.embodied cognition | lexical semantics | magnetoencephalography | MEG | mismatch negativity T he old debate on localization of cognitive functions in the brain was recently reinvigorated with the advent of a concept of mirror neurons and a closely related framework of grounded cognition (1-8). The mirror neuron theory stemmed from a seminal discovery of neurons that activate equally when a specific action is performed by the tested individual or when observing the same action performed by others, giving a strong neurophysiological proof for the concept of comprehension and learning through simulation (for a review, see ref. 1). This is enabled by the presence of perception-action circuits in the brain that can provide motor areas with multimodal sensory information (2). An array of findings in mirror neuron and related research strongly suggest that the motor system is not merely a "slave" or an "output" of any central processing, but that it also takes an active role in perception and comprehension of external events. In cognitive science, which had suggested the emergence of concepts from individual experiences long before these neurophysiological discoveries (3-5), a similar strand of research led to a more general framework of "grounding" (or "embodiment") of cognitive functions and representations in bodily sensations and actions, which was supported through a range of behavioral and neurophysiological experiments (6-8).Nowhere these approaches resonated more than in the neuroscience of language. Following breakthrough neurological studies of the 19th century (9, 10), the human language function was for many decades confined to a small set of cortical areas in the left hemisphere. More recent research, however, challenged these views in favor of linguistic representations distributed over a range of brain areas, which span beyond the core language cortices of B...

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Section: Methodsmentioning

confidence: 99%

Automatic ultrarapid activation and inhibition of cortical motor systems in spoken word comprehension

Shtyrov

Butorina

Nikolaeva

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

119

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“…This distributed source analysis does not make a priori assumptions about underlying generators and attempts to minimize the overall activity that can account for the recorded electric potentials (Ilmoniemi, 1993). Realistic head shape and three-layer (skin-skull-cortex) boundaryelement model (BEM) were used to account for current spread through the head tissues.…”

Section: Methodsmentioning

confidence: 99%

Rapid Cortical Plasticity Underlying Novel Word Learning

Shtyrov¹,

Nikulin²,

Pulvermüller³

2010

J. Neurosci.

112

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Humans are unique in developing large lexicons as their communication tool. To achieve this, they are able to learn new words rapidly. However, neural bases of this rapid learning, which may be an expression of a more general cognitive mechanism, are not yet understood. To address this, we exposed our subjects to familiar words and novel spoken stimuli in a short passive perceptual learning session and compared automatic brain responses to these items throughout the learning exposure. Initially, we found enhanced activity for known words, indexing the ignition of their underlying memory traces. However, just after 14 min of learning exposure, the novel items exhibited a significant increase in response magnitude matching in size with that to real words. This activation increase, as we would like to propose, reflects rapid mapping of new word forms onto neural representations. Similar to familiar words, the neural activity subserving rapid learning of new word forms was generated in the left-perisylvian language cortex, especially anterior superior-temporal areas. This first report of a neural correlate of rapid learning suggests that our brain may effectively form new neuronal circuits online as it gets exposed to novel patterns in the sensory input. Understanding such fast learning is key to the neurobiological explanation of the human language faculty and learning mechanisms in general.

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“…In the cases meeting these criteria, source localization was performed using L1 minimumnorm estimation [10,16,29]. The L1 estimation results in a current distribution with the smallest integral of the absolute value of the current density that could generate the measured magnetic field and provides a minimum-norm current estimate (MCE [30]) with location and strength information for the current sources at each time point.…”

Section: Methodsmentioning

confidence: 99%

Activation in the anterior left auditory cortex associated with phonological analysis of speech input: localization of the phonological mismatch negativity response with MEG

Kujala

Alho

Ilmoniemi

et al. 2004

Cognitive Brain Research

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The spatio-temporal dynamics of cortical activation underlying auditory word recognition, particularly its phonological stage, was studied with whole-head magnetoencephalography (MEG). Subjects performed a visuo-auditory priming task known to evoke the phonological mismatch negativity (PMN) response that is elicited by violations of phonological expectancies. Words and non-words were presented in separate conditions. In each of the 318 trials, the subjects first saw a word/non-word (e.g., 'cat') that was soon followed by a prime letter (e.g., 'h'). Their task was to replace mentally the sound of the first letter of the word/non-word with the prime letter, thus resulting in a new word/non-word (e.g., 'hat'). Finally, an auditory word/nonword either matching or mismatching with the anticipated item was presented. In most subjects, a PMNm followed by a later, N400m-like negativity was obtained in the left hemisphere to the mismatching auditory stimuli. A similar response pattern was obtained in the right hemisphere only in a few subjects. Source localization of the N1m, an index of acoustic analysis, and the PMNm and N400m-like responses was performed using L1 minimum-norm estimation. In the left hemisphere, the PMNm source for the words was significantly more anterior than the source of the N400m-like response; for the non-words, the PMNm source was significantly more anterior than the sources of the N1m and the N400m-like response. These results suggest that the lefthemisphere neuronal networks involved in sub-lexical phonological analysis are at least partly different from those responsible for the earlier (acoustic) and later (whole item) processing of speech input.

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Models of source currents in the brain

Cited by 67 publications

References 24 publications

Automatic ultrarapid activation and inhibition of cortical motor systems in spoken word comprehension

Automatic ultrarapid activation and inhibition of cortical motor systems in spoken word comprehension

Rapid Cortical Plasticity Underlying Novel Word Learning

Activation in the anterior left auditory cortex associated with phonological analysis of speech input: localization of the phonological mismatch negativity response with MEG

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