Measurement of Photon Statistics with Live Photoreceptor Cells

We analyzed the electrophysiological response of an isolated rod photoreceptor of Xenopus laevis under stimulation by coherent and pseudo-thermal light sources. Using the suction electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudo-thermal light of the same intensity and also differences in signal-to-noise ratios and second order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.Comment: 6 pages, 7 figure

Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods

The Ca2+-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca2+-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca2+ dynamics, indicating that recoverin is a significant Ca2+ buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca2+-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin

A pattern-recognition theory of search in expert problem solving

Understanding how look-ahead search and pattern recognition interact is one of the important research questions in the study of expert problem-solving. This paper examines the implications of the template theory (Gobet & Simon, 1996a), a recent theory of expert memory, on the theory of problem solving in chess. Templates are "chunks" (Chase & Simon, 1973) that have evolved into more complex data structures and that possess slots allowing values to be encoded rapidly. Templates may facilitate search in three ways: (a) by allowing information to be stored into LTM rapidly; (b) by allowing a search in the template space in addition to a search in the move space; and (c) by compensating loss in the "mind's eye" due to interference and decay. A computer model implementing the main ideas of the theory is presented, and simulations of its search behaviour are discussed. The template theory accounts for the slight skill difference in average depth of search found in chess players, as well as for other empirical data

Optimizing the vertebrate vestibular semicircular canal: could we balance any better?

The fluid-filled semicircular canals (SCCs) of the vestibular system are used by all vertebrates to sense angular rotation. Despite masses spanning seven decades, all mammalian SCCs are nearly the same size. We propose that the SCC represents a sensory organ that evolution has `optimally designed'. Four geometric parameters are used to characterize the SCC, and `building materials' of given physical properties are assumed. Identifying physical and physiological constraints on SCC operation, we find that the most sensitive SCC has dimensions consistent with available data.Comment: 4 pages, 3 figure

Influence of Acute Water Ingestion on Bioelectrical Impedance Analysis Estimates of Body Composition

Body composition estimation is a significant component of health and fitness assessments. Multi-frequency bioelectrical impedance analysis (MFBIA) uses multiple electrical frequencies that travel through body tissues in order to estimate fluid content and body composition. Prior to body composition assessments, it is common to implement a wet fast (i.e., a fasting period that allows water intake); however, the influence of a wet fast as compared to a dry fast (i.e., disallowing water intake) is relatively unknown. PURPOSE: To determine the effects of acute water consumption on MFBIA body composition estimates. METHODS: A randomized crossover study was conducted in 16 adults (8 F, 8 M; age: 22.0 ± 2.9 y; height: 173.6 ± 9.9 cm; weight: 74.3 ± 21.6 kg; body mass index: 24.6 ± 4.7; body fat % [BF%]: 16.7 ± 8.1%). On two occasions, participants reported to the laboratory after an overnight food and fluid fast. After a baseline MFBIA assessment, participants either consumed 11 mL/kg of bottled water (W condition) or consumed no fluid as the control (CON condition). The 11 ml/kg dose of water corresponded to absolute intakes of 531 to 1360 mL. After the water consumption time point, MFBIA tests were performed every 10 minutes for one hour. Participants stood upright for the entire research visit. MFBIA estimates of body mass (BM), fat mass (FM), fat-free mass (FFM), and BF% were analyzed using 2 x 7 (condition x time) analysis of variance with repeated measures, follow-up pairwise comparisons, and evaluation of the partial eta-squared (ηp2) effect sizes. RESULTS: No variables differed between conditions at baseline. Condition x time interactions were present for all variables (BM: pp2=0.89; FM: p=0.0008, ηp2=0.30; BF%: p=0.005, ηp2=0.23) except FFM (p=0.69, ηp2=0.03). Follow-up testing indicated that BM was ~0.6 kg higher in W as compared to CON at all post-baseline time points (pp2=0.32), regardless of condition. CONCLUSION: Up to one hour after ingestion, acute water intake was exclusively detected as increased FM by MFBIA. This contrasts with the common belief that ingesting water prior to bioimpedance tests would result in inflated FFM and decreased BF%. Since body composition estimates never returned to baseline within the hour after water ingestion, it is not clear how long this effect would persist. These results suggest acute water ingestion can produce an inflation of MFBIA body fat estimates for at least one hour. These results indicate that water intake during fasting periods should be considered as part of pre-assessment standardization

Body Fat Gain Automatically Increases Lean Mass by Changing the Fat-Free Component of Adipose Tissue

Estimating alterations in lean mass in response to various training interventions is a primary concern for many investigations. However, previous reports have suggested that lean mass estimates from weight loss interventions may be significantly altered by attempting to correct for changes in the fat-free component of adipose tissue (FFAT). This component, consisting primarily of water and protein, has been estimated as ~15% of adipose tissue (AT) mass. While a preliminary examination of this correction method has been conducted in the instance of weight loss, it has yet to be investigated after a period of purposeful weight gain and resistance training. PURPOSE: To examine the impact of corrections for FFAT on estimates of lean mass accretion during a period of weight gain and resistance training. METHODS: Twenty-one resistance trained males underwent 6 weeks of supervised training and followed a hypercaloric diet in order to elicit weight gain. Body composition was assessed pre- and post-intervention via dual energy x-ray absorptiometry (DXA). AT was estimated using DXA-derived fat mass (FM) in the equation: AT = FM/0.85. FFAT was then estimated via the equation: FFAT = 0.15 × AT. Lastly, FFAT was subtracted from DXA-derived lean mass (LMDXA) to yield the new corrected lean mass value (cLM). Changes in LMDXA and cLM in response to the training intervention were calculated, and dependent samples T-tests were employed to determine if significant differences were present between changes in LMDXA and cLM. RESULTS: Significant differences (p ≤ 0.001) were noted for estimates of LM gain, with a larger increase observed for LMDXA as compared to cLM (LMDXA :2.42 ± 1.58kg; cLM: 2.14 ± 1.65kg). CONCLUSION: Correcting DXA-derived LM for the fat-free component of adipose tissue reduces the magnitude of LM accretion after a period of weight gain. However, while LM estimates did significantly differ, the small degree to which they differed indicates questionable practical relevance of such corrections in future investigations

Impact of Fluid Consumption on Estimates of Intracellular, Extracellular, and Total Body Water from Multi-Frequency Bioelectrical Impedance Analysis

Multi-frequency bioelectrical impedance analysis (MFBIA) is able to distinguish between total body water (TBW), extracellular water (ECW) and intracellular water (ICW). Low-frequency currents are thought to primarily pass through ECW, while high-frequency currents pass through all body fluids (i.e., TBW). ICW can then be estimated by subtracting ECW from TBW. As such, MFBIA may have utility for monitoring health conditions resulting in water retention within specific fluid compartments. However, the sensitivity of fluid estimates from MFBIA is not fully established. PURPOSE: To evaluate the effects of acute fluid ingestion on body water estimates produced by a MFBIA analyzer. METHODS: Sixteen adults (8 F, 8 M; age: 22.0 ± 2.9 y; height: 173.6 ± 9.9 cm; weight: 74.3 ± 21.6 kg; body fat %: 16.7 ± 8.1%) participated in a randomized crossover study consisting of two conditions: 1) no fluid ingestion (control; C); and 2) acute ingestion of 11 mL/kg of bottled water (W). In both conditions, participants reported to the laboratory after an overnight food and fluid fast for serial assessments using 8-point standing MFBIA. An initial MFBIA assessment was performed at baseline, followed by a 5-minute period during which water was ingested (W condition) or the participant continued to rest in the lab (C condition). Beginning 10 minutes after this time period, participants were assessed by MFBIA every 10 minutes for one hour. Participants stood upright for the entirety of each research visit. Analysis of variance with repeated measures was used to examine differences in MFBIA estimates of body mass (BM), TBW, ECW, and ICW between conditions and across time. Follow-up pairwise comparisons were performed and partial eta-squared (ηp2) effect sizes were calculated. RESULTS: A group-by-time interaction was present for BM (pp2: 0.89) but not TBW (p=0.74; ηp2: 0.03), ECW (p=0.85; ηp2: 0.02), or ICW (p=0.87; ηp2: 0.05). Follow-up indicated that BM did not differ between conditions at baseline but was ~0.6 ± 0.2 kg higher in the W condition as compared to C at all post-baseline time points (pp2: 0.29 to 0.38). No significant effects were observed for ECW. CONCLUSION: The lack of change in body fluids with acute water ingestion likely indicates that: 1) within one hour, ingested water has not been assimilated into body fluids to the extent that it is detectable by MFBIA; or 2) the quantity of fluid ingestion is below the detection limits of the MFBIA analyzer. In support of the first point, it is likely that bioelectrical currents do not penetrate the gastrointestinal tract, meaning fluids contained therein are unlikely to be detected by MFBIA as fluids