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Cortical modulations increase in early sessions with brain-machine interface.

Zacksenhouse M, Lebedev MA, Carmena JM, O'Doherty JE, Henriquez C, Nicolelis MA - PLoS ONE (2007)

Bottom Line: We conclude that the enhanced modulations are related to computational tasks that are significant especially in novel motor contexts.Although the function and neuronal mechanism of the enhanced cortical modulations are open for further inquiries, we discuss their potential role in processing execution errors and representing corrective or explorative activity.These representations are expected to contribute to the formation of internal models of the external actuator and their decoding may facilitate BMI improvement.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Mechanical Engineering, Technion, Haifa, Israel. mermz@tx.technion.ac.il

ABSTRACT

Background: During planning and execution of reaching movements, the activity of cortical motor neurons is modulated by a diversity of motor, sensory, and cognitive signals. Brain-machine interfaces (BMIs) extract part of these modulations to directly control artificial actuators. However, cortical modulations that emerge in the novel context of operating the BMI are poorly understood.

Methodology/principal findings: Here we analyzed the changes in neuronal modulations that occurred in different cortical motor areas as monkeys learned to use a BMI to control reaching movements. Using spike-train analysis methods we demonstrate that the modulations of the firing-rates of cortical neurons increased abruptly after the monkeys started operating the BMI. Regression analysis revealed that these enhanced modulations were not correlated with the kinematics of the movement. The initial enhancement in firing rate modulations declined gradually with subsequent training in parallel with the improvement in behavioral performance.

Conclusions/significance: We conclude that the enhanced modulations are related to computational tasks that are significant especially in novel motor contexts. Although the function and neuronal mechanism of the enhanced cortical modulations are open for further inquiries, we discuss their potential role in processing execution errors and representing corrective or explorative activity. These representations are expected to contribute to the formation of internal models of the external actuator and their decoding may facilitate BMI improvement.

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Inhomogeneous Poisson process and implied variance distribution.
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pone-0000619-g001: Inhomogeneous Poisson process and implied variance distribution.

Mentions: Spike-trains can be considered as realizations of point processes [20], [21]. The number of spikes recorded in a bin of size b, Nb, depends on the average bin-rate in that bin Λb, which is modulated by the encoded signals, as depicted in Figure 1 (upper diagram). However this dependence is stochastic and the variance of the spike-count Var[Nb] may differ from the variance of the bin-rate Var[Λb]. While the variance of the spike-count can be measured directly, it is the variance of the bin-rate that is of interest here because it reflects signal modulations. In order to investigate these modulations, we defined the percent overall modulation (POM) as:(1)Since the variance of the bin-rate cannot be measured directly, the POM cannot be estimated without further assumptions. However, instead of restricting the analysis to firing-rate modulations that involve specific modulating signals, we made only basic assumptions about the nature of the spikes trains. In particular, we assumed that the spike trains are realizations of inhomogeneous Poisson processes, which are the simplest point processes that can describe rate modulations. We further generalized the analysis to additive noise models whose variance is proportional to the mean.


Cortical modulations increase in early sessions with brain-machine interface.

Zacksenhouse M, Lebedev MA, Carmena JM, O'Doherty JE, Henriquez C, Nicolelis MA - PLoS ONE (2007)

Inhomogeneous Poisson process and implied variance distribution.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1919433&req=5

pone-0000619-g001: Inhomogeneous Poisson process and implied variance distribution.
Mentions: Spike-trains can be considered as realizations of point processes [20], [21]. The number of spikes recorded in a bin of size b, Nb, depends on the average bin-rate in that bin Λb, which is modulated by the encoded signals, as depicted in Figure 1 (upper diagram). However this dependence is stochastic and the variance of the spike-count Var[Nb] may differ from the variance of the bin-rate Var[Λb]. While the variance of the spike-count can be measured directly, it is the variance of the bin-rate that is of interest here because it reflects signal modulations. In order to investigate these modulations, we defined the percent overall modulation (POM) as:(1)Since the variance of the bin-rate cannot be measured directly, the POM cannot be estimated without further assumptions. However, instead of restricting the analysis to firing-rate modulations that involve specific modulating signals, we made only basic assumptions about the nature of the spikes trains. In particular, we assumed that the spike trains are realizations of inhomogeneous Poisson processes, which are the simplest point processes that can describe rate modulations. We further generalized the analysis to additive noise models whose variance is proportional to the mean.

Bottom Line: We conclude that the enhanced modulations are related to computational tasks that are significant especially in novel motor contexts.Although the function and neuronal mechanism of the enhanced cortical modulations are open for further inquiries, we discuss their potential role in processing execution errors and representing corrective or explorative activity.These representations are expected to contribute to the formation of internal models of the external actuator and their decoding may facilitate BMI improvement.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Mechanical Engineering, Technion, Haifa, Israel. mermz@tx.technion.ac.il

ABSTRACT

Background: During planning and execution of reaching movements, the activity of cortical motor neurons is modulated by a diversity of motor, sensory, and cognitive signals. Brain-machine interfaces (BMIs) extract part of these modulations to directly control artificial actuators. However, cortical modulations that emerge in the novel context of operating the BMI are poorly understood.

Methodology/principal findings: Here we analyzed the changes in neuronal modulations that occurred in different cortical motor areas as monkeys learned to use a BMI to control reaching movements. Using spike-train analysis methods we demonstrate that the modulations of the firing-rates of cortical neurons increased abruptly after the monkeys started operating the BMI. Regression analysis revealed that these enhanced modulations were not correlated with the kinematics of the movement. The initial enhancement in firing rate modulations declined gradually with subsequent training in parallel with the improvement in behavioral performance.

Conclusions/significance: We conclude that the enhanced modulations are related to computational tasks that are significant especially in novel motor contexts. Although the function and neuronal mechanism of the enhanced cortical modulations are open for further inquiries, we discuss their potential role in processing execution errors and representing corrective or explorative activity. These representations are expected to contribute to the formation of internal models of the external actuator and their decoding may facilitate BMI improvement.

Show MeSH
Related in: MedlinePlus