Biomedical subjects

Agnes S Chan

Publications and source records attributed to Agnes S Chan.

At least 19 recordsLinked to original sources

PubMed2007

Quantitative electroencephalographic profiles for children with autistic spectrum disorder.

The present study examined quantitative electroencephalographic (QEEG) profile for children with autistic spectrum disorder (ASD). Five-minute QEEG data were obtained from 90 normal controls (NCs) and 66 children with ASD. Spectrum analyses revealed that ASD children showed significantly less relative alpha and more relative delta than NC. Specifically, 26% of ASD children and 2% of NCs showed 1.5 SDs of relative alpha below the normative mean. Children with this QEEG profile had 17 times the risk of having ASD than those without such a profile. Sensitivity and specificity of relative alpha were 91% and 73%, respectively. Split-half cross-validation yielded a sensitivity of 76%.

Adolescent↗

PubMed2006

Pre-activating the mesial temporal lobe facilitates learning.

While numerous neuroimaging studies have been conducted to examine brain activities associated with different cognitive tasks, few have focused on the effects of temporary increase in blood oxygen level on subsequent cognitive performance. The present study aimed to study this temporary hemodynamic change on subsequent learning. Using the novel picture encoding task (NPET) to activate the hippocampus, the present functional magnetic resonance imaging study showed that the level of blood oxygen level-dependent signals in the mesial temporal lobe associated with NPET positively predicted memory performance after engaging in the NPET for normal controls and patients with temporal lobe epilepsy. In addition, patients demonstrated significantly greater improvement on memory performance than normal controls. Though the improvement was transient, these results provided a neuro-physiological evidence to support our previous hypothesis that the functioning of a specific brain region can be facilitated by performing a task mediated by the same region.

Adolescent↗

PubMed2006

Differentiating Autistic Children With Quantitative Encephalography: A 3-Month Longitudinal Study.

The present study used a single-channel quantitative electroencephalographic (EEG) assessment to differentiate autistic children from normal control subjects. One hundred five normal and 17 autistic children participated in the study. In addition to amplitude measures of the frequency bands of delta, theta, alpha, sensorimotor rhythm, and beta and the theta to beta ratio, intra- (6 minutes) and intersessional (3 months) consistencies were also examined. The results indicated that autistic children showed significantly higher quantitative EEG amplitudes in many of the frequency bands than normal children; furthermore, their quantitative EEG activities were found to be relatively unstable within a 6-minute session compared with normal children. Discriminant function analyses revealed that absolute sensorimotor rhythm and beta amplitudes were the best predictors that correctly differentiated autistic children from normal children in the present sample, with a high accuracy rate of 95.2%. In addition, quantitative EEG measurements of normal and autistic children were found to be generally consistent across the 3-month period. (J Child Neurol 2006;21:391-399; DOI 10.2310/7010.2006.00094).

Journal Article↗

PubMed2006

Language lateralization of Chinese-English bilingual patients with temporal lobe epilepsy: a functional MRI study.

Functional MRI was used to examine language lateralization of Chinese characters and English words associated with temporal lobe epilepsy (TLE) in Chinese-English bilinguals with left or right TLE. The results suggest that the neural basis of processing Chinese and English seems to be different, as normal controls demonstrated left hemispheric lateralization in reading English words but bi-hemispheric lateralization in reading Chinese characters. This difference in the neural bases of Chinese and English processing was found to affect the patterns in change-of-language processing associated with TLE. That is, whereas left-TLE patients were more likely than right-TLE patients to demonstrate a bi-hemispheric language involvement in reading English, both left- and right-TLE patients demonstrated primarily bilateral hemispheric involvement for reading Chinese characters.

Adolescent↗

PubMed2006

Effects of illness duration on memory processing of patients with temporal lobe epilepsy.

PURPOSE: To examine the effects of illness duration on the neural processing of memory in patients with temporal lobe epilepsy (TLE) by using functional MRI. METHODS: Twenty-three TLE patients (16 left, seven right) performed a complex visual scene-encoding task during functional MRI. Region-of-interest (ROI) analyses were used to quantity functional activation in the mesial temporal and frontal lobes. The patients' verbal and visual memory performances were evaluated by standardized neuropsychological tests. Analyses included group comparison and correlations of duration of epilepsy with functional activation and memory performance. RESULTS: Compared with normal controls, TLE patients demonstrated reduced activation bilaterally in the mesial temporal lobe (p=0.003), and the reduction was more pronounced on the ipsilateral side of the seizure focus. Moreover, a longer duration of illness was associated with fewer voxels activated in both the left (p=0.038) and right (p=0.017) mesial temporal lobe. Furthermore, the duration of illness was found to be significantly and negatively correlated with both verbal (p=0.020) and visual (p=0.000) memory functioning. CONCLUSIONS: TLE seems to affect the memory processes in the mesial temporal lobes progressively (i.e., the longer the duration of illness, the lower the brain activation). In turn, the reduction of brain activation negatively affects memory functioning. Finally, the reduction is not limited to the side of seizure but also is observed in the contralateral hemisphere.

Adolescent↗

PubMed2006

Bilateral frontal activation associated with cutaneous stimulation of elixir field: an FMRI study.

Elixir Field, or Dan Tian, is the area where energy is stored and nourished in the body according to traditional Chinese medicine (TCM). Although Dan Tian stimulation is a major concept in Qigong healing and has been practiced for thousands of years, and while there are some recent empirical evidence of its effect, its neurophysiological basis remains unknown. We used functional magnetic resonance imaging (fMRI) to study brain activations associated with external stimulation of the lower Elixir Field in ten normal subjects, and compared the results with the stimulation of their right hands. While right-hand stimulation resulted in left postcentral gyrus activation, stimulation of the lower Elixir Field resulted in bilateral activations including the medial and superior frontal gyrus, middle and superior temporal gyrus, thalamus, insula, and cingulate gyrus. These findings suggest that stimulation of the Elixir Field is not only associated with activation of the sensory motor cortex but also with cortical regions that mediate planning, attention, and memory.

Adult↗

PubMed2006

Differentiating autistic children with quantitative encephalography: a 3-month longitudinal study.

Autistic Disorder↗

PubMed2005

Association between mind-body and cardiovascular exercises and memory in older adults.

OBJECTIVES: To compare the memory function of older adults who regularly practiced mind-body (MB) or cardiovascular (CV) exercises with that of those who did not engage in regular exercise. Older adults who engaged in both types of exercise were also included to examine the combined effects. DESIGN: Cross-sectional study between 2002 and 2003. SETTING: Older adults from a local community in Hong Kong. PARTICIPANTS: One hundred forty adults aged 56 and older. MEASUREMENTS: The Hong Kong List Learning Test was used to assess the memory of all participants. It is a clinically validated Chinese verbal-memory test that measures various aspects of memory processing, including learning, retention, and retrieval abilities. MB and CV exercises were defined using three dimensions: motion speed, emphasis on relaxing the mind, and conscious control of movement. RESULTS: Older adults who practiced MB or CV exercises demonstrated a similar level of memory function, and their learning and memory was better than that of individuals who did not exercise regularly. Those who practiced both types of exercises outperformed all other groups, even after corrected for the total hours of exercise. Although memory change across age was found in older adults who did not exercise, this trend was not observed in individuals who practiced MB exercises. CONCLUSION: Practicing both MB and CV exercises appears to have a combined effect that might help to preserve memory in older adults. In addition, MB exercises may be considered as an alternative training for older adults who cannot practice strenuous physical exercise.

Aged↗

PubMed2004

Phase II study of alpha-tocopherol in improving the cognitive function of patients with temporal lobe radionecrosis.

BACKGROUND: Radiotherapy is an important treatment modality for brain tumors and is the standard radical treatment for nasopharyngeal carcinoma (NPC). However, the treatment is not free of side effects, and one possible neurologic sequela is the occurrence of temporal lobe radionecrosis (TLN) associated with cognitive dysfunction. Currently, there is no effective intervention to improve patients' cognitive performance. METHODS: Twenty-nine patients with TLN after radiotherapy for NPC were recruited on a voluntary basis. Among them, 19 patients (15 males and 4 females) received a megadose of alpha-tocopherol (vitamin E) (2000 international units per day) for 1 year, whereas the other 10 (5 males and 5 females) served as control patients. Their cognitive function (i.e., global cognitive ability, attention, memory, language, and executive function) was evaluated by a battery of neuropsychological tests before and after treatment. RESULTS: Significant improvement in global cognitive ability (P = 0.035) and memory (verbal: P = 0.036; visual: P = 0.007) occurred among patients in the treatment group after a 1-year medication period. In addition, the executive function of the treatment group improved significantly (P = 0.04). No difference was found between the two groups with respect to attention or language. CONCLUSIONS: The current investigation was a preliminary study on the effect of alpha-tocopherol on the cognitive function of patients with TLN after radiotherapy for NPC. In view of the absence of effective treatment for patients with cerebral radionecrosis, alpha-tocopherol has the potential to be a complementary intervention for patients with cognitive dysfunction due to TLN.

Aged↗

PubMed2004

The executive clock drawing task (CLOX) is a poor screening test for executive dysfunction in Chinese elderly patients with subcortical ischemic vascular disease.

Executive dysfunction (ED) is a prominent feature of subcortical ischemic vascular disease. A screening test for ED is lacking among Chinese. The objective of the study is to investigate the validity and reliability of a Chinese version of the Executive clock drawing task (CLOX) in screening ED among Chinese elderly patients with small subcortical infarct (SSI). The Chinese version of CLOX correlated with MMSE, CDRS I/P, and WCST perseverative errors. However, multivariate regression analysis showed that only education (R(2) change=0.22, p < 0.001 ) and MMSE (R(2) change=0.35, p < 0.001), but none of the standard executive function tests, significantly accounted for the variance in the CLOX. Test-retest (r=0.84) and inter-rater reliability (r=0.84) were high for the CLOX. Conclusions. Although the CLOX is reliable, it is not valid in detecting ED in Chinese elderly patients with SSI.

Age Factors↗

PubMed2004

Confrontation naming in Chinese patients with left, right or bilateral brain damage.

Confrontation naming of 52 unilateral or bilateral brain-damaged Chinese patients were examined with a modified version of the Boston Naming Test (BNT). Chinese patients with left or right hemisphere lesions, contrary to studies on English speakers, demonstrated similar levels of naming impairments, supporting the notion that English and Chinese are mediated by different neuroprocessing systems. In addition, the psychometric properties of the BNT on Chinese population were examined. While the test demonstrated satisfactory internal consistency and discriminant validity, level of education was found to be a significant factor affecting participants' performance. A cut-off score of 24 in spontaneous naming yielded a sensitivity of 73.1% and specificity of 75.3% in differentiating normal from brain-damaged participants, suggesting that the modified BNT is applicable to the Chinese population.

Adolescent↗

PubMed2004

Neuroanatomical basis in the temporal lobes for processing living things.

Category-specific impairment in living things was examined in patients with temporal lobe damage to investigate whether specific neuroanatomical regions could be identified in processing the knowledge of specific categories. Tasks involving more effortful retrieval naming and less effortful attribute judgment were administered to 3 groups of patients with either bilateral, unilateral left, or unilateral right temporal lobe damage. Category-specific impairment in living things was observed for patients with unilateral or bilateral damage, results that are consistent with previous findings. Depending on its site and extent, the damage in the temporal lobe might lead to deficits in processing or loss of semantic knowledge for living things. Therefore, intact category-specific semantic processes may involve associations among different neural substrates in the temporal lobe.

Aged↗

PubMed2003

Impact of radionecrosis on cognitive dysfunction in patients after radiotherapy for nasopharyngeal carcinoma.

BACKGROUND: Cognitive dysfunction is common in patients who develop radionecrosis after receiving radiotherapy for nasopharyngeal carcinoma (NPC). However, the impact of the location and volume of radionecrosis on cognitive dysfunction remains unclear. The authors found a significant association between the severity of cognitive impairment and the volume of radionecrosis; in turn, the volume of radionecrosis was affected by patient age at time radiotherapy was completed. METHODS: Fifty patients with NPC who received radiotherapy were evaluated by a battery of neuropsychologic tests of cognitive function. The brain lesion volume was quantified, and the lesion locations were identified by standardized brain templates. The results of the neuropsychologic tests were correlated with lesion volume. Gender, education, age at the completion of radiotherapy, brain volume, total dose, and fractional dose were evaluated as risk factors for lesion volume. RESULTS: Lesion volume was correlated significantly with the severity of cognitive deficits. Larger left-hemisphere lesions were correlated with lower verbal memory (from P < 0.001 to P = 0.008) and language abilities (from P = 0.001 to P = 0.018), whereas larger right-hemisphere lesions were associated with worse visual memory (from P = 0.009 to P = 0.039). Finally, patients who received radiotherapy at a younger age had smaller lesion volumes (P < 0.001). CONCLUSIONS: The volume and location of radionecrosis had an influential impact on the pattern of cognitive impairment found in patients with NPC, and patient age at the time radiotherapy was completed appeared to affect the volume of radionecrosis found after radiotherapy.

Adult↗

PubMed2003

Memory impairment in humans after bilateral damage to lateral temporal neocortex.

The hippocampus and its adjacent medial temporal regions are crucial for episodic memory. However, it is far less obvious whether other temporal regions beyond the medial part are important for memory processing. The memory performance of a group of patients with bilateral lesions over the lateral temporal lobe sparing the hippocampus was assessed and compared with that of patients with relatively spared cortex and patients with bilateral damage to the lateral temporal lobe and the hippocampus. The results demonstrate that bilateral damage to the lateral temporal lobe results in memory impairment across verbal and visual modalities.

Adult↗

PubMed2003

Clinical validity of the Chinese version of Mattis Dementia Rating Scale in differentiating dementia of Alzheimer's type in Hong Kong.

The present study aimed to examine the clinical validity and applicability of the Chinese version of Mattis Dementia Rating Scale (CDRS) for elderly Chinese individuals. The scale was found to have good reliability with internal consistency ranging from 0.7 to 0.9. Its significant correlation with the Chinese version of Mini-Mental State Examination (CMMSE) suggested satisfactory construct validity of the scale. The discriminant validity of the CDRS in differentiating Alzheimer's disease (AD) patients and Normal Control (NC) elderly was also supported by the Receiver Operating Characteristics (ROC) analysis. Several cut-off points were presented for different clinical or research applications, and formulas to adjust for the age and educational level of the CDRS total score were provided. The Initiation/Perseveration and Memory subscales were suggested to be an abbreviated version of the CDRS for a quick screening. The present results also showed the association between the impairment of the CDRS performance and the progress of the AD.

Age Factors↗

PubMed2003

Verbal learning in Alzheimer's dementia.

Many recent findings in Western countries suggest that episodic recall is the most sensitive discriminator between patients with mild Alzheimer disease (AD) and the normal elderly, while semantic memory tends best to differentiate between moderate and severe AD patients. The present study is the first to examine in detail the episodic memory of Chinese AD patients in Hong Kong with a locally developed list learning test, comparing procedures that do or do not encourage the use of semantic organization. The performance of 28 AD patients was compared to that of 30 normal controls. AD patients did significantly worse in terms of acquisition and retention and also benefited significantly less from external organization cues. In the discriminant function analysis, the rate of forgetting in the random condition and the total retention score in the blocked condition were found to be the best predictors for differentiating between AD patients and controls. On the other hand, in the differentiation between mild and moderate AD, semantic clustering in the blocked condition was found to be the best predictor. Results of the present study were discussed in the light of the previous findings reported in the Western countries and the neuropathological changes of AD patients.

Aged↗

PubMed2003

Things aren't as bad as they seem: a comment on Storms et al. (2003).

G. Storms, T. Dirikx, J. Saerens, S. Verstraeten, and P. P. De Deyn (2003) criticized the use of scaling techniques, in proposing "semantic storage deficits" in Alzheimer's disease and schizophrenic patients in some studies, arguing that most reported multidimensionalscaling (MDS) models for patients were not adequately fit and did not differ from models generated by random data. The studies cited by G. Storms et al. were reexamined and all available data relevant to their claim were compared. A more complete review revealed somewhat different conclusions; it showed that many of the MDS models seem to meet the criteria of adequate fit, and it does not seem to support the notion that patients' performance is close to random. Suggestions are made to improve the validity of scaling analysis in neuropsychological studies.

Alzheimer Disease↗

PubMed2003

Music training improves verbal but not visual memory: cross-sectional and longitudinal explorations in children.

The hypothesis that music training can improve verbal memory was tested in children. The results showed that children with music training demonstrated better verbal but not visual memory than did their counterparts without such training. When these children were followed up after a year, those who had begun or continued music training demonstrated significant verbal memory improvement. Students who discontinued the training did not show any improvement. Contrary to the differences in verbal memory between the groups, their changes in visual memory were not significantly different. Consistent with previous findings for adults (A. S. Chan, Y. Ho, & M. Cheung, 1998), the results suggest that music training systematically affects memory processing in accordance with possible neuroanatomical modifications in the left temporal lobe.

Adolescent↗