Biomedical subjects

Kyoung-Min Lee

Publications and source records attributed to Kyoung-Min Lee.

14 recordsLinked to original sources

PubMed2007

Effect of the number of response alternatives on brain activity in response selection.

It is well-known in motor control literature that a response time (RT) increases as a logarithmic function of the number of response alternatives (NA) (Hick's law). In this study, we identified neural correlates for this relationship using event-related functional MRI and a choice finger-movement task. Behaviorally, average RTs of all subjects increased as a logarithmic function of the NA in accordance with the law. From a voxel-wise search for brain areas where the activity was correlated with NA and thence the RT, a positive correlation was found at the posterior cingulate and left superior frontal gyri, whereas a negative correlation was observed at areas in bilateral inferior parietal lobules. This differential modulation by the task context, namely, the NA available for a choice response with identical stimulus and response, indicates that these regions are involved in various aspects of response selection, intentional retrieval of motor program, or spatial expectancy.

Adult↗

PubMed2006

Differential correlation of frontal and parietal activity with the number of alternatives for cued choice saccades.

The time taken to choose a response appropriate for a cue increases with the number of potential response options (Hick's law). We used this temporal constraint of choice behavior in event-related fMRI experiments to identify brain areas carrying out the translation from a cue stimulus to response: Since the process takes longer with more alternatives, the activity of the areas would increase in correlation with the number of alternatives (NA) available at the time of choice decision. During a choice saccade task in which one target is selected among many alternatives based on the color of a cue in the center, the frontal eye fields (FEF) and intraparietal sulcus (IPS) were activated. Within these regions, signals were correlated with NA at the medial part of the FEF and the posterior part of the IPS, but not at the lateral FEF and anterior IPS. This suggests a functional differentiation within each cortical region. Furthermore, given the separate fronto-parietal projections linking sub-regions that are alike in NA-correlation, cognitive steps for choice decision may occur in different networks of the sub-regions: i.e., the stimulus-response translation step in a network of the posterior IPS and medial FEF, and response execution in the anterior IPS/lateral FEF network.

Adult↗

PubMed2006

Patient-reported assessment of quality care at end of life: development and validation of Quality Care Questionnaire-End of Life (QCQ-EOL).

Our goal was to validate an instrument with which terminally ill patients could evaluate the quality of care they receive at the end of life (EOL). Questionnaire development followed a four-phase process: item generation and reduction, construction, pilot testing, and field-testing. Using relevance and priority criteria and pilot testing, we developed a 16-item questionnaire. Factor analyses of data from 235 patients resulted in the Quality Care Questionnaire-End of Life (QCQ-EOL) covering dignity-conserving care, care by health care professionals, individualised care, and family relationships. All subscales and total scores showed high internal consistency (Cronbach alpha range, 0.73-0.89). The ability of total score and selective subscale scores clearly differentiated patients on the basis of clinical situation, sense of dignity, and general rating of care quality. Correlations of scores between patients and caregivers were substantial. The QCQ-EOL can be adopted to assess the quality of care received by terminally ill patients.

Adult↗

PubMed2006

Symbolic cue-driven activity in superior colliculus neurons in a peripheral visual choice task.

Recent evidence implicates the superior colliculus (SC) in cognitive processes, such as target selection and control of spatial attention, in addition to the execution of saccadic eye movements. We report here the presence of a cognitive response in some cells in the SC in a task that requires the long-term association of spatial location with an arbitrary color. In this study, using a visual choice response task, we demonstrate that visuomotor neurons in the SC were activated by the appearance of a central symbolic cue delivered outside of the visual response fields of the recorded neurons. This procedure ensures that cognitively generated activity in these SC cells is not confounded with modulation of activity from previous visual stimuli that appeared in the response field of the neurons. The experiments suggest that cognitive signals can activate SC cells by themselves instead of only being able to modulate activities already evoked by visual events. Furthermore, a substantial fraction of these cells accurately reflected cue-aligned target selection in advance of saccade initiation. Our results add further support to other studies that have demonstrated that internally generated signals exist in SC cells.

Animals↗

PubMed2005

Brain activation during music listening in individuals with or without prior music training.

The present study investigated activation during listening to music with and without a task in female musicians and non-musicians. Five subjects with long musical training for a mean period of 19+/-1 years (musician group) and five subjects with no training in musical instruments (non-musician group) were imaged in a 1.5T scanner, while they simply listened to short segments of piano pieces (LIS), and while they performed a distorted tune test, designed using the same pieces (DTT). A significant group effect with higher signals in the musician group was observed in the right superior and middle temporal gyri, the right inferior frontal gyrus, and the left supramarginal gyrus. A task effect with higher signals during DTT was observed in the left sensorimotor cortex, where the interaction between the task and group effects was also significant. Thus, the pattern of brain activation differed depending on tasks when identical music stimuli were used, and more importantly, comparable music tasks activated the brain differently depending on prior musical training of subjects.

Acoustic Stimulation↗

PubMed2005

Readout of higher-level processing in the discharge of superior colliculus neurons.

The discharge of neurons in the deeper layers of the superior colliculus (SC) was studied while monkeys performed two visual discrimination tasks that required different amounts of cognitive processing. In a search paradigm the animal's task was to saccade to the location of an odd-colored stimulus located in an array of distractors of uniform color (pop-out visual search). The visual stimuli remained on the screen as the discrimination process distinguished target from distractors. In a choice response task the color of a central cue signaled which stimulus from a previously presented array of colored stimuli was to be the target of a saccade. The stimulus array was turned off well before the central cue was presented. Most neurons showed activity aligned on both the visual input and the motor response in single-target tasks. Many of these same neurons showed additional discharge that was correlated with the required higher-level decision processes in both of these more natural visual tasks. In the case of pop-out search the SC has been shown to be functionally involved in the decision processes. The cue-aligned activity in SC in the choice response task is surprising because no transient visual stimulus appeared in the response field of the neuron.

Animals↗

PubMed2004

Properties of saccades generated as a choice response.

Since Hick's original description, many subsequent studies have confirmed the logarithmic relationship that exists between response time and the number of alternatives (NA) for a choice response. In the present study a novel paradigm was used to quantify saccade response time as a function of NA. Normal subjects were required to make a saccade to the remembered location of a visual target whose color was specified by a centrally located cue. The paradigm thus required a stimulus-response transformation similar to that used by Hick. The results show that, when such a transformation was required, a logarithmic relationship was found for saccadic response time. The use of a color-to-location paradigm to study saccade choice response time produced an unexpected additional result that may provide insight into the neural organization of the saccadic system. When the number of alternative choice responses was large (4 or 8), subjects frequently made a two-saccade response instead of a single saccade to the correct location. The first movement in such a sequence was in the correct direction, but was hypometric. A second movement then followed which moved the eyes onto the correct location. These results suggest dynamic dissociations in the mechanisms underlying the triggering of saccades and the specification of their metrics.

Adult↗

PubMed2004

Musical training-induced functional reorganization of the adult brain: functional magnetic resonance imaging and transcranial magnetic stimulation study on amateur string players.

We used the combined technique of functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) to observe changes that occur in adult brains after the practice of stringed musical instruments. We carried out fMRI on eight volunteers (aged 20-22 years): five novices and three individuals who had discontinued practice for more than 5 years. The motor paradigm contained a repetitive lift-abduction/fall-adduction movement of the left/right little finger, carried out with maximum efforts without pacing. The sensory paradigm was to stimulate the same little finger using a string. In parallel to the fMRI acquisition, TMS motor maps for the little finger were obtained using a frameless stereotactic neuronavigation system. After the baseline study, each participant began to learn a stringed instrument. Newly developed fMRI activations for the left little finger were observed 6 months after practice at multiple brain regions including inferior parietal lobule, premotor area (PMA), left precuneus, right anterior superior temporal gyrus, and posterior middle temporal gyrus. In contrast, new activations were rarely observed for the right little finger. The TMS study revealed new motor representation sites for the left little finger in the PMA or supplementary motor area (SMA). Unexpectedly, TMS motor maps for the right little finger were reduced significantly. Among new fMRI activations for sensory stimuli of the left little finger, the cluster of highest activation was located in the SMA. Collectively, these data provide insight into orchestrated reorganization of the sensorimotor and temporal association cortices contributing to the skillful fingering and musical processing after the practice of playing stringed instruments.

Adult↗

PubMed2004

Functional MRI comparison between reading ideographic and phonographic scripts of one language.

Brain activation during reading of phonographic (Hangul) and ideographic (Hanja) words is compared using functional MRI by taking advantage of the bi-scriptal system of the Korean language. To examine the psycholinguistic difference, i.e., phonographic vs. ideographic, separately from other differences due to Hanja being a secondary script, we made a control comparison between Hangul and the English alphabet, another phonographic and secondary script. Interaction analysis between the two comparisons revealed that the right fusiform gyrus and adjacent temporo-occipital region, among others, seem more specifically involved in processing ideographic scripts. On the other hand, regions in bilateral inferior parietal lobules were more active with Hangul reading than Hanja. This is consistent with the notion that reading the phonographic script may involve the assembled phonology route in addition to the addressed lexical route, whereas reading the ideographic script may not involve the former.

Adult↗

PubMed2004

Change in phase synchronization of local field potentials in anesthetized rats after chronic dopamine depletion.

In order to investigate temporal characteristics of oscillatory neural activity and the effect of chronic dopamine depletion on it, local field potentials were measured in anesthetized rats without or with a 6-OHDA lesion at either the ventral tegmental area or the substantia nigra compacta, using a pair of electrodes that were separated by 120 microm. Coupling of neural activity in this mesoscopic scale was measured by a synchronization index that quantified the distribution of differences in instantaneous phase between the two potentials recorded. Phase synchrony was significantly stronger at deep basal ganglia sites, more so than at cortical sites, over a gamma range (30-120 Hz) in normal rats. After chronic dopamine depletion, this synchrony was no longer observable, especially after a substantia nigra lesion, while there was an increase in phase synchrony in the cortex at a lower frequency band (10 Hz). These findings are consistent with previously reported findings that the effect of dopaminergic innervation on oscillatory neural activity varies from synchronizing to desynchronizing, depending on the structure innervated and the frequency of the oscillation.

Anesthesia↗

PubMed2002

Alteration of functional neuroanatomy of simple object memory in medial temporal lobe epilepsy patients.

Using H2 15O PET, we examined the neuroanatomy associated with a simple form of episodic memory in patients with right or left medial temporal lobe epilepsy and normal healthy controls. When line drawings of common objects were memorized and tested after a 30 min delay, no behavioral difference was found between the patient groups and the controls. However, the patients with epilepsy showed greater cortical activations than the control group on the side ipsilateral to the epileptic focus. rCBF in the anterior thalamic region was enhanced in patients relative to the control group. The results showed that long-term dysfunction of the medial temporal lobe might reinforce alternative memory pathways and recruit a distributed cortical network ipsilateral to their epilepsy focus.

Adult↗

PubMed2002

Phonological agraphia after superior temporal gyrus infarction.

BACKGROUND: Phonological agraphia refers to a condition in which the ability to write nonwords to dictation is impaired, while writing words to dictation is preserved, as is oral repetition of the words and nonwords. This condition has been regarded as reflecting a disconnection within the phonological writing system, and previous neurolinguistic correlations suggested that the anterior-inferior supramarginal gyrus was a crucial link within the system. SETTING: A neurology department of a university hospital. PATIENT: A 51-year-old right-handed man presented with speech disturbances. On initial evaluation of his language, his deficit was consistent with that of conduction aphasia, which improved rapidly to an apparently normal level. A subsequent detailed examination of oral and written repetition of words and nonwords revealed a rather selective form of phonological agraphia. A magnetic resonance imaging scan of his brain showed a focal ischemic lesion at the left posterior superior temporal gyrus and at the underlying white matter. CONCLUSIONS: In contrast to most previously described patients, this patient showed a selective impairment of phonological agraphia in association with a focal infarction restricted to the left posterior superior temporal gyrus, suggesting that this region of the brain is an important node within a wider network of areas that subserve the phonological route for writing.

Agraphia↗

PubMed2002

Arithmetic operation and working memory: differential suppression in dual tasks.

The relationship between arithmetic function and working memory was examined using a dual-task paradigm for either phonological or visuo-spatial suppression. Simultaneous phonological rehearsal significantly delayed the performance of multiplication but not subtraction, whereas holding an image in the mind delayed subtraction but not multiplication. This result indicates that arithmetic function is related to working memory in a subsystem-specific manner: multiplication is more closely linked to phonological loop and subtraction to visuo-spatial sketchpad. Whereas this is not compatible with the notion that arithmetic is done on a unitary, amodal representation of numbers, it provides support for the triple-code and/or the modular processing models on human numerical cognition in which number representations are specific for input/output modality and arithmetic types.

Adult↗

PubMedDate not supplied

Characteristics of glucose metabolism in the visual cortex of amblyopes using positron-emission tomography and statistical parametric mapping.

BACKGROUND: The effects of amblyopia on the glucose metabolism in the visual cortex in the resting state are evaluated, the asymmetry of glucose metabolism in the ipsilateral and the contralateral occipital lobes was examined by comparing the number of hypometabolic pixels in both occipital lobes, and the correlation between this asymmetry and the results of the ophthalmologic tests was evaluated. METHODS: Eleven amblyopes (7 anisometropic and 4 strabismic) and 12 normal subjects were studied with their eyes open, but without any further visual stimulus using F-18-fluorodeoxyglucose positron-emission tomography (PET) and statistical parametric mapping. Ophthalmologic tests including stereoacuity, contrast sensitivity function, monocular optokinetic nystagmus, and visual evoked potential (VEP) were measured. RESULTS: Compared to normal subjects, glucose metabolism decreased in Brodmann area (BA) 17, BAs 18/19, both inferior temporal lobes (BAs 37 and 20), and the superior parietal lobe (BA 7) in amblyopic patients, regardless of strabismic or anisometropic amblyopia. The laterality index of the hypometabolic pixels in the occipital lobe closely correlated with the asymmetry in the latency time of VEP (r = 0.82, P <0.05). CONCLUSION: These results suggest that PET imaging of glucose metabolism can provide a functional mapping of the visual cortex in human amblyopia.

Adolescent↗