Biomedical subjects

Kuan H Kho

Publications and source records attributed to Kuan H Kho.

5 recordsLinked to original sources

PubMed2007

Involuntary language switching in two bilingual patients during the Wada test and intraoperative electrocortical stimulation.

We present two bilingual patients without language disorders in whom involuntary language switching was induced. The first patient switched from Dutch to English during a left-sided amobarbital (Wada) test. Functional magnetic resonance imaging yielded a predominantly left-sided language distribution similar for both languages. The second patient switched from French to Chinese during intraoperative electrocortical stimulation of the left inferior frontal gyrus. We conclude that the observed language switching in both cases was not likely the result of a selective inhibition of one language, but the result of a temporary disruption of brain areas that are involved in language switching. These data complement the few lesion studies on (involuntary or unintentional) language switching, and add to the functional neuroimaging studies of switching, monitoring, and controlling the language in use.

Adult↗

PubMed2006

Figuring out drawing-induced epilepsy.

Rare reflex epilepsies are a clinical curiosity but may also give insight into neurocognitive processes. The authors present a patient whose seizures were precipitated by drawing but not by writing. This dissociation complements previous reports on selective impairment of writing. EEG revealed a focus in the right frontal lobe with parietal spread. This is in accord with current cognitive and neural network models of drawing.

Adult↗

PubMed2006

Towards human BCI applications based on cognitive brain systems: an investigation of neural signals recorded from the dorsolateral prefrontal cortex.

One of the critical issues in brain-computer interface (BCI) research is how to translate a person's intention into brain signals for controlling computer programs. The motor system is currently the primary focus, where signals are obtained during imagined motor responses. However, cognitive brain systems are also attractive candidates, in that they may be more amenable to conscious control, yielding better regulation of magnitude and duration of localized brain activity. We report on a proof of principle study for the potential use of a higher cognitive system for BCI, namely the working memory (WM) system. We show that mental calculation reliably activates the WM network as measured with functional magnetic resonance imaging (fMRI). Moreover, activity in the dorsolateral prefrontal cortex (DLPFC) indicates that this region is active for the duration of mental processing. This supports the notion that DLPFC can be activated, and remains active, at will. Further confirmation is obtained from a patient with an implanted electrode grid for diagnostic purposes, in that gamma power within DLPFC increases during mental calculation and remains elevated for the duration thereof. These results indicate that cortical regions involved in higher cognitive functions may serve as a readily self-controllable input for BCI applications. It also shows that fMRI is an effective tool for identifying function-specific foci in individual subjects for subsequent placement of cortical electrodes. The fact that electrocorticographic (ECoG) signal confirmed the functional localization of fMRI provides a strong argument for incorporating fMRI in BCI research.

Attention↗

PubMed2005

Meralgia paresthetica after strenuous exercise.

We present three patients with signs and symptoms of meralgia paresthetica (MP) after long-distance walking and cycling. No other possible causes of MP, such as trauma or exogenous compression, were present. A neuropathy of the lateral femoral cutaneous nerve was confirmed in all patients with somatosensory evoked potentials. We propose that conduction block due to local ischemia during repetitive muscle stretching was the probable cause for the neuropathy.

Adult↗

PubMed2005

Discrepant findings for Wada test and functional magnetic resonance imaging with regard to language function: use of electrocortical stimulation mapping to confirm results. Case report.

The Wada test is still considered the gold standard for determining the language-dominant hemisphere prior to brain surgery. The authors report on a 34-year-old right-handed woman whose Wada test results indicated that the right hemisphere was dominant for language. In contrast, functional magnetic resonance (fMR) imaging was indicative of bilaterally represented language functions. Activation in the left hemisphere demonstrated on fMR imaging was most pronounced in the Broca area. Importantly, fMR imaging results in this area were confirmed on electrocortical stimulation mapping. These contradictory findings indicated that a right hemispherre dominance for language according to the Wada test should be questioned and verified using electrocortical stimulation. Nonetheless, the question remains whether involvement of these areas in the left frontal hemisphere is critical for language, as these were spared during surgery.

Adult↗