Single trial discrimination of individual finger movements on one hand: A combined MEG and EEG study

Authors:

• Fanny Quandt

• Christoph Reichert

• Hermann Hinrichs

• Hans-Jochen Heinze

• Robert T. Knight

• Jochem W. Rieger

Date: 2011

DOI: 10.1016/j.neuroimage.2011.11.053

PubMed: 22155040

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Abstract:

It is crucial to understand what brain signals can be decoded from single trials with different recording techniques for the development of Brain-Machine Interfaces. A specific challenge for non-invasive recording methods are activations confined to small spatial areas on the cortex such as the finger representation of one hand. Here we study the information content of single trial brain activity in non-invasive MEG and EEG recordings elicited by finger movements of one hand. We investigate the feasibility of decoding which of four fingers of one hand performed a slight button press. With MEG we demonstrate reliable discrimination of single button presses performed with the thumb, the index, the middle or the little finger (average over all subjects and fingers 57%, best subject 70%, empirical guessing level: 25.1%). EEG decoding performance was less robust (average over all subjects and fingers 43%, best subject 54%, empirical guessing level 25.1%). Spatiotemporal patterns of amplitude variations in the time series provided best information for discriminating finger movements. Non-phase-locked changes of mu and beta oscillations were less predictive. Movement related high gamma oscillations were observed in average induced oscillation amplitudes in the MEG but did not provide sufficient information about the finger's identity in single trials. Importantly, pre-movement neuronal activity provided information about the preparation of the movement of a specific finger. Our study demonstrates the potential of non-invasive MEG to provide informative features for individual finger control in a Brain-Machine Interface neuroprosthesis.

Damage to the prefrontal cortex impairs familiarity but not recollection memory

Authors:

• Mariam Aly

• Andrew P. Yonelinas

• Mark M. Kishiyama

• Robert T. Knight

Date: 2011

PubMed: 21827792

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Abstract:

Frontal lobe lesions impair recognition memory but it is unclear whether the deficits arise from impaired recollection, impaired familiarity, or both. In the current study, recognition memory for verbal materials was examined in patients with damage to the left or right lateral prefrontal cortex. Words were incidentally encoded under semantic or phonological orienting conditions, and recognition memory was tested using a 6-point confidence procedure. Receiver operating characteristics (ROCs) were examined in order to measure the contributions of recollection and familiarity to recognition memory. In both encoding conditions, lateral prefrontal cortex damage led to a deficit in familiarity but not recollection. Similar deficits were observed in left and right hemisphere patients. The results indicate that the lateral prefrontal cortex plays a critical role in the monitoring or decision processes required for accurate familiarity-based recognition responses.

Dynamic communication and connectivity in frontal networks

Authors:

• Bradley Voytek

• Robert T. Knight

Date: 2011

DOI: 10.1093/acprof:oso/9780199791569.003.0028

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Abstract:

How do we maintain a stable percept of the world in the face of the powerful drive of neuroplasticity in both health and disease? This dichotomy forms one of the most fundamental unanswered questions in neuroscience concerning the balance between the dynamic, plastic underpinnings of our neurobiology and the relative stability of our cognition. Th e brain undergoes massive changes in size, morphology, and connectivity during normal development and aging as well as in response to brain injury, yet we can maintain a relatively stable sense of cognition and self during the lifespan. Human brains, each with over 100 billion neurons, develop similarly despite the wide variations in environment and experience. However, within the bounds of this stability there exists a wide range of variability and capacity for change. Here we will discuss the role of neuroplasticity in frontal lobe-dependent cognition by examining the localization of attention and memory functions in the brain and how these seemingly fixed locations may reflect flexible neural networks that change communication properties as required by behavior.

Cortical Spatio-temporal Dynamics Underlying Phonological Target Detection in Humans

Authors:

• Edward F. Chang

• Erik Edwards

• Srikantan S. Nagarajan

• Noa Fogelson

• Sarang S. Dalal

• Ryan T. Canolty

• Heidi E. Kirsch

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2011

DOI: 10.1162/jocn.2010.21466

PubMed: 20465359

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Abstract:

Selective processing of task-relevant stimuli is critical for goal-directed behavior. We used electrocorticography to assess the spatio-temporal dynamics of cortical activation during a simple phonological target detection task, in which subjects press a button when a prespecified target syllable sound is heard. Simultaneous surface potential recordings during this task revealed a highly ordered temporal progression of high gamma (HG, 70-200 Hz) activity across the lateral hemisphere in less than 1 sec. The sequence demonstrated concurrent regional sensory processing of speech syllables in the posterior superior temporal gyrus (STG) and speech motor cortex, and then transitioned to sequential task-dependent processing from prefrontal cortex (PFC), to the final motor response in the hand sensorimotor cortex. STG activation was modestly enhanced for target over nontarget sounds, supporting a selective gain mechanism in early sensory processing, whereas PFC was entirely selective to targets, supporting its role in guiding response behavior. These results reveal that target detection is not a single cognitive event, but rather a process of progressive target selectivity that involves large-scale rapid parallel and serial processing in sensory, cognitive, and motor structures to support goal-directed human behavior.

Electrophysiological evidence for different inhibitory mechanisms when stopping or changing a planned response

Authors:

• Ulrike M. Krämer

• Robert T. Knight

• Thomas F. Münte

Date: 2011

DOI: 10.1162/jocn.2010.21573

PubMed: 20849230

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Abstract:

People are able to adapt their behavior to changing environmental contingencies by rapidly inhibiting or modifying their actions. Response inhibition is often studied in the stop-signal paradigm that requires the suppression of an already prepared motor response. Less is known about situations calling for a change of motor plans such that the prepared response has to be withheld but another has to be executed instead. In the present study, we investigated whether electrophysiological data can provide evidence for distinct inhibitory mechanisms when stopping or changing a response. Participants were instructed to perform in a choice RT task with two classes of embedded critical trials: Stop signals called for the inhibition of any response, whereas change signals required participants to inhibit the prepared response and execute another one instead. Under both conditions, we observed differences in go-stimulus processing, suggesting a faster response preparation in failed compared with successful inhibitions. In contrast to stop-signal trials, changing a response did not elicit the inhibition-related frontal N2 and did not modulate the parietal mu power decrease. The results suggest that compared with changing a response, additional frontal and parietal regions are engaged when having to inhibit a response.