Dataset Information

Decoding spoken words using local field potentials recorded from the cortical surface.

ABSTRACT: Pathological conditions such as amyotrophic lateral sclerosis or damage to the brainstem can leave patients severely paralyzed but fully aware, in a condition known as 'locked-in syndrome'. Communication in this state is often reduced to selecting individual letters or words by arduous residual movements. More intuitive and rapid communication may be restored by directly interfacing with language areas of the cerebral cortex. We used a grid of closely spaced, nonpenetrating micro-electrodes to record local field potentials (LFPs) from the surface of face motor cortex and Wernicke's area. From these LFPs we were successful in classifying a small set of words on a trial-by-trial basis at levels well above chance. We found that the pattern of electrodes with the highest accuracy changed for each word, which supports the idea that closely spaced micro-electrodes are capable of capturing neural signals from independent neural processing assemblies. These results further support using cortical surface potentials (electrocorticography) in brain-computer interfaces. These results also show that LFPs recorded from the cortical surface (micro-electrocorticography) of language areas can be used to classify speech-related cortical rhythms and potentially restore communication to locked-in patients.

SUBMITTER: Kellis S

PROVIDER: S-EPMC2970568 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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Decoding spoken words using local field potentials recorded from the cortical surface.

Kellis Spencer S Miller Kai K Thomson Kyle K Brown Richard R House Paul P Greger Bradley B

Journal of neural engineering 20100901 5

Pathological conditions such as amyotrophic lateral sclerosis or damage to the brainstem can leave patients severely paralyzed but fully aware, in a condition known as 'locked-in syndrome'. Communication in this state is often reduced to selecting individual letters or words by arduous residual movements. More intuitive and rapid communication may be restored by directly interfacing with language areas of the cerebral cortex. We used a grid of closely spaced, nonpenetrating micro-electrodes to r ...[more]

PMID: 20811093

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Project description:Numerous studies report brain potential evidence for the anticipation of specific words during language comprehension. In the most convincing demonstrations, highly predictable nouns exert an influence on processing even before they appear to a reader or listener, as indicated by the brain's neural response to a prenominal adjective or article when it mismatches the expectations about the upcoming noun. However, recent studies suggest that some well-known demonstrations of prediction may be hard to replicate. This could signal the use of data-contingent analysis, but might also mean that readers and listeners do not always use prediction-relevant information in the way that psycholinguistic theories typically suggest. To shed light on this issue, we performed a close replication of one of the best-cited ERP studies on word anticipation (Van Berkum, Brown, Zwitserlood, Kooijman & Hagoort, 2005; Experiment 1), in which participants listened to Dutch spoken mini-stories. In the original study, the marking of grammatical gender on pre-nominal adjectives ('groot/grote') elicited an early positivity when mismatching the gender of an unheard, highly predictable noun, compared to matching gender. The current pre-registered study involved that same manipulation, but used a novel set of materials twice the size of the original set, an increased sample size (N = 187), and Bayesian mixed-effects model analyses that better accounted for known sources of variance than the original. In our study, mismatching gender elicited more negative voltage than matching gender at posterior electrodes. However, this N400-like effect was small in size and lacked support from Bayes Factors. In contrast, we successfully replicated the original's noun effects. While our results yielded some support for prediction, they do not support the Van Berkum et al. effect and highlight the risks associated with commonly employed data-contingent analyses and small sample sizes. Our results also raise the question whether Dutch listeners reliably or consistently use adjectival inflection information to inform their noun predictions.

Project description:OBJECTIVE:Action potentials and local field potentials (LFPs) recorded in primary motor cortex contain information about the direction of movement. LFPs are assumed to be more robust to signal instabilities than action potentials, which makes LFPs, along with action potentials, a promising signal source for brain-computer interface applications. Still, relatively little research has directly compared the utility of LFPs to action potentials in decoding movement direction in human motor cortex. APPROACH:We conducted intracortical multi-electrode recordings in motor cortex of two persons (T2 and [S3]) as they performed a motor imagery task. We then compared the offline decoding performance of LFPs and spiking extracted from the same data recorded across a one-year period in each participant. MAIN RESULTS:We obtained offline prediction accuracy of movement direction and endpoint velocity in multiple LFP bands, with the best performance in the highest (200-400 Hz) LFP frequency band, presumably also containing low-pass filtered action potentials. Cross-frequency correlations of preferred directions and directional modulation index showed high similarity of directional information between action potential firing rates (spiking) and high frequency LFPs (70-400 Hz), and increasing disparity with lower frequency bands (0-7, 10-40 and 50-65 Hz). Spikes predicted the direction of intended movement more accurately than any individual LFP band, however combined decoding of all LFPs was statistically indistinguishable from spike-based performance. As the quality of spiking signals (i.e. signal amplitude) and the number of significantly modulated spiking units decreased, the offline decoding performance decreased 3.6[5.65]%/month (for T2 and [S3] respectively). The decrease in the number of significantly modulated LFP signals and their decoding accuracy followed a similar trend (2.4[2.85]%/month, ANCOVA, p = 0.27[0.03]). SIGNIFICANCE:Field potentials provided comparable offline decoding performance to unsorted spikes. Thus, LFPs may provide useful external device control using current human intracortical recording technology. ( CLINICAL TRIAL REGISTRATION NUMBER:NCT00912041.).

Dataset Information

Decoding spoken words using local field potentials recorded from the cortical surface.

Publications

Decoding spoken words using local field potentials recorded from the cortical surface.

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