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Biomedical subjects

B B Lee

Publications and source records attributed to B B Lee.

At least 73 records · Page 4Linked to original sources
PubMed1999

Activity of prefrontal neurons during location and color delayed matching tasks.

Many cells in prefrontal cortex show enhanced activity prior to movement onset in delayed or memory-guided saccade tasks. This activity is a possible neural correlate of spatial attention and working memory. The goal of this study was to determine whether delay activity is evoked when non-spatial cues such as color are used to guide saccades. Monkeys were trained on a saccade target selection task in which they were cued for either the location or color of the rewarded target. When the location of the target was specified explicitly, many cells showed visual responses and delay activity that were spatially selective. Color selective visual responses or delay activity were both rare and weak. However, for many cells, spatially selective delay activity could be evoked when color was used to specify the location of the target. These results indicate that color is capable of eliciting spatially selective activity from cells that have no overt color selectivity.

Animals↗
PubMed1999

A possible selective impairment of magnocellular function in compression of the anterior visual pathways.

Two parallel visual systems, the magnocellular (M) and parvocellular (P) pathways, originate from different types of retinal ganglion cells, and are known to be segregated in different portions of the pregeniculate visual pathways. Their relative contribution to two main cortical streams, dorsal and ventral, is still under discussion, but it is reasonable to suppose that selective damage to the M or P subcortical system might interfere with specific aspects of processing within one or the other cortical system. Using two different apparent-motion tasks, we compared the performance of patients affected by compression of the ventral part of the pregeniculate visual pathways with that of normal controls. In the first task, observers detected small displacements of a low-contrast vertical bar, while in the second task they estimated the visible persistence of moving dots. In the first task, patients were impaired with parafoveal displays, especially in the temporal portion of the visual field. In the second task, patients showed reduced suppression of visible persistence at long, but not at short, exposure durations. Three considerations support the hypothesis that these results represent a selective impairment of the M system. First, M axons are more likely to suffer from compression, particularly in the case of a mass growing from below since they are known to occupy a ventral subpial position in the optic chiasm and tract. Second, the performance of patients with a ventral compression is consistent with the characteristics of the response properties of P ganglion cells, which have previously been shown to exhibit elevated and unmodulated thresholds for displacement detection in the macaque monkey. Third, such patients are less sensitive to the inhibitory signals that suppress visible persistence, which probably originate in the M system.

Adenoma↗
PubMed1999

Single units and sensation: a retrospect.

The single-neuron doctrine is reexamined, and the search for causal links between single units and sensation reviewed. Although several decades of single-unit recording have been very successful in elucidating physiological mechanisms, linking signals from a single cell and perception has progressed at a slower rate. Nevertheless, analysing the activity of single neurons has achieved significant gains and remains the most promising level for elucidation of processing algorithms in the visual system. At the subcortical level, the conclusion that signals from just a single cell can carry enough information for some kinds of performance remains (almost) valid. Under carefully controlled conditions, just a few impulses in a few retinal ganglion cells are an adequate signal for the cortex to initiate a behavioural response. Elucidating cortical codes has been more difficult, and evidence exists suggesting the sharing of responsibility for a task among cell assemblies; how large these assemblies are, and how to test for them neurophysiologically, remains a challenge.

Humans↗
PubMed1999

Combined spinal-epidural analgesia in labour: comparison of two doses of intrathecal bupivacaine with fentanyl.

We have compared intrathecal bupivacaine 1.25 mg and fentanyl 25 micrograms (group A) with bupivacaine 2.5 mg and fentanyl 25 micrograms (group B), for combined spinal-epidural analgesia in 49 labouring parturients in a prospective, randomized, double-blind study. Onset and quality of analgesia were similar in both groups, with median visual analogue scale pain scores of 0 achieved in 5-10 min. Median duration of analgesia was longer in group B (median 120 (range 90-120) min) compared with group A (75 (75-105) min) (P = 0.013). Median upper sensory level was higher in group B compared with group A at 15 min (T6-7 vs T11, P = 0.003) and at 30 min (T6 vs T11-12; P = 0.001). Motor block was greater in group B: seven patients had a modified Bromage score > or = 1 compared with none in group A at 15 min (P = 0.017). Group B also had a greater decrease in arterial pressure. Patient-midwife satisfaction scores and other side effects were similar. We conclude that intrathecal bupivacaine 1.25 mg with fentanyl 25 micrograms provided analgesia of similar onset and quality compared with bupivacaine 2.5 mg and fentanyl 25 micrograms. Although the duration of analgesia was shorter, the incidences of motor block and hypotension were less with the smaller dose.

Adult↗
PubMed1999

Venous dynamics in leg lymphedema.

To determine whether there is anatomical and/or functional impairment to venous return in patients with lymphedema, we examined venous dynamics in 41 patients with unilateral leg lymphedema. A Volometer was used for computer analysis of leg volume, a color Duplex Doppler scanner was used to determine deep vein patency and skin thickness, and Air-plethysmography was used to assess ambulatory venous pressure, venous volume, venous filling index and the ejection fraction. In the lymphedematous leg, volume and skin thickness were uniformly increased (126.4 +/- 21.3% and 156.9 +/- 44.5%) (mean +/- S.D.), respectively. The ambulatory venous pressure was also increased (134 +/- 60.7%) as was the venous volume (124.5 +/- 37.5%), and the venous filling index (134.5 +/- 50.5%). The ejection fraction was decreased (94.9 +/- 26.1%). Greater leg volume correlated with increased venous volume and venous filling index (values = 0.327, 0.241, respectively) and decreased ejection fraction (r = -0.133). Increased subcutaneous thickness correlated with increased venous filling index and venous volume (r = 0.307, 0.126, respectively) and decreased ejection fraction (r = -0.202). These findings suggest that soft tissue edema from lymphatic stasis gradually impedes venous return which in turn aggravates the underlying lymphedema.

Female↗
PubMed1999

Changes in lymphatic function after complex physical therapy for lymphedema.

Twenty-two extremities of 19 lymphedema patients (6 arms, 16 legs) were treated by 2 weeks of complex physical therapy (CPT) and self home maintenance therapy (bandage/wearing of elastic garment and exercise). In addition to the clinical response of volume reduction before and 3 months after CPT, we analyzed the functional changes of the peripheral lymphatic system by use of lymphoscintigraphy (LS). Before CPT, the main LS findings of lymphedema included dermal backflow (100%), absent or faintly visualized regional lymph nodes (95.5%), presence of collateral lymphatic vessels (68.2%), and no or barely visualized lymphatic vessels (27.3%). LS findings suggesting improved lymphatic function after CPT were a decrease in dermal backflow (72.7%), an increase in radioisotope uptake by lymphatic vessels (27.3%), and an increase in radioisotope uptake by lymph nodes (9.1%). 81.8% of limbs showed improved lymphoscintigraphic findings and no change in 9.1%. In the others (9.1%), LS findings appeared worse. There was, however, no correlation between LS "improvement" and the amount of limb volume reduction.

Antimony↗
PubMed1998

Post-receptoral mechanisms of colour vision in New World primates.

Diurnal platyrrhines, both di- and trichromats, have magnocellular (M-) and parvocellular (P-) retinal ganglion cells which are morphologically very similar to those found in catarrhines. Catarrhine central P ganglion cells contact single midget bipolar cells, which contact single cones. Physiological recordings of retinal ganglion cells of dichromatic Cebus monkeys showed very similar cell properties to the catarrhine macaque, except that P ganglion cells lacked colour-opponency. We describe the presence of single-headed midget bipolar cells in the Cebus retina. These midget bipolar cells have axon terminal sizes in the same range as the dendritic tree sizes of P ganglion cells as far as 2 mm of retinal eccentricity. This result supports the view that, as in catarrhines, central P ganglion cells of platyrrhines receive input from single midget bipolar cells which in turn, receive input from single cones. This finding is consistent with the idea that a P pathway with one-to-one connectivity was present in the anthropoid ancestor before the divergence between catarrhines and platyrrhines.

Action Potentials↗
PubMed1998

Comparative retinal physiology in anthropoids.

During the last decade it has become clear that colour vision in platyrrhines (New World monkeys) differs from the uniform trichromatic pattern normally found in catarrhines (Old World monkeys, apes and human). Colour vision in most platyrrhine species is polymorphic, with many dichromatic individuals. The comparison of response properties in retinal ganglion cells and lateral geniculate cells between catarrhines and playrrhines elucidates how the evolution of trichromatic colour vision influenced the post-receptoral processing. We find that spatial and temporal processing is very similar in the platyrrhine and catarrhine retina, strongly suggesting that the retinal structure and function, found in living anthropoids, was already present in their common ancestor.

Action Potentials↗
PubMed1998

Intraoperative complications of 1000 phacoemulsification procedures: a prospective study.

PURPOSE: To determine the frequency and nature of intraoperative complications of endocapsular phacoemulsification cataract surgery. SETTING: Dalcross Private Hospital and the Departments of Ophthalmology, Concord Hospital and Prince of Wales Hospital, Sydney, Australia. METHODS: This prospective study included the first 1000 cases of planned endocapsular phacoemulsification cataract surgery performed by an experienced surgeon. A standardized proforma was completed at the time of surgery. Data recorded included pre-existing ocular abnormalities, duration of surgery, nuclear sclerosis grade, and intraoperative complications. RESULTS: Major complications comprised posterior capsule tears with vitreous loss (1.4%), isolated posterior capsule tears (0.7%), and zonulysis (0.1%). Minor complications included anterior capsule tears (3.8%), iris prolapse (0.6%), and ciliary body incision (0.2%). There was a significant trend toward complications as the nuclear sclerosis grade increased. The incidence of major complications was 9.3% in the first 150 cases and 0.9% in the last 850. This represents a relative risk of 9.9 (95% confidence interval 4.2 to 23.0) of a major complication occurring in the first 150 compared with the later 850 cases. CONCLUSION: The frequency of major and minor complications fell sharply after the first 150 operations and was maintained. This study may provide a guide for beginning phacoemulsification surgeons and a basis for experienced surgeons to compare their performance outcomes.

Adult↗
PubMed1998

Chamfered margin effects on occlusal microleakage of primary molar Class I composite resin restorations in vitro.

Recent clinical studies have suggested that composite resin may be an effective restorative material for the restoration of Class I preparation in primary molars. The primary objective of this study was to assess the effects in vitro of a chamfered margin on occlusal microleakage of class I posterior composite resin restorations in primary molars. Two cavity preparations (conventional and modified) were compared by using forty extracted primary molars. The modified class I preparation as described in this study showed no occlusal microleakage and recommended to be further studied clinically. The difference between these two groups was analyzed by using the Fisher Exact Probability Test and was statistically significant.

Child↗
PubMed1998

Excision of subcutaneous tissue and deep muscle fascia for advanced lymphedema.

In advanced peripheral lymphedema particularly involving the legs, complex physical therapy (massage/bandage-wrapping compression, remedial exercises, and maintenance use of a low stretch elastic compression garment), is not uniformly successful. In six patients with morbid lymphedema of the legs, we described our positive experience using a modified Auchincloss/Homans excisional operation.

Adipose Tissue↗
PubMed1997

Rod inputs to macaque ganglion cells.

The strength of rod inputs to ganglion cells was assessed in the macaque retina at retinal positions within 3-15 deg eccentricity. The experimental paradigm used temporally modulated heterochromatic lights whose relative phase was varied. This paradigm provided a sensitive test to detect rod input. In parvocellular (PC) pathway cells, the gain of the cone-driven signal decreased with decrease in luminance. At 2 td a weak rod response, of a few impulses per second for 100% rod modulation, was revealed in about 60% of cells. For blue-on cells, the cone-driven response also decreased with retinal illuminance, but no rod response could be found. In magnocellular (MC) pathway cells, rod input was much more apparent. Responses became rod dominated at and below 20 td; we cannot exclude rod intrusion at higher retinal illuminances. Responsivity was maintained even at low retinal illuminances. Temporal-frequency dependent rod-cone interactions were observed in MC-pathway cells. Rod responses were of longer latency than cone responses, but there was no evidence of any difference in rod latency between parvocellular and magnocellular pathways.

Animals↗