Taiki Takahashi

Discounting Delayed and Probabilistic Monetary Gains and Losses by Smokers of Cigarettes

RationaleNicotine dependence has been associated with impulsivity and discounting delayed/uncertain outcomes.ObjectivesThis study had two main objectives: (1) to examine the relationship between the number of cigarettes consumed per day and the degree to which delayed and uncertain monetary gains and losses are discounted by smokers, and (2) to determine the relationship between the estimated dose of nicotine intake per day and the degree to which four types of discounting occur.MethodsTwenty seven habitual smokers and 23 never smokers participated in this experiment. They were required to choose between immediate and delayed monetary rewards (or losses), or between guaranteed and probabilistic rewards (or losses).ResultsThe degree to which delayed monetary gains were discounted was significantly and positively correlated with both the number of cigarettes smoked and the estimated dose of nicotine intake per day. Conversely, there was no relationship between smoking and the remaining three types of discounting. Also, mild smokers in our sample did not differ from never smokers in discounting monetary gains or losses.ConclusionsIn general, our results suggest that both the frequency of nicotine self-administration, as well as the dosage, are positively associated with greater delay discounting of gains. One neuropsychopharmacological explanation for this effect is that chronic nicotine intake may induce neuroadaptation of the neural circuitry involved in reward processing.

Corticosterone acutely prolonged N‐methyl‐d‐aspartate receptor‐mediated Ca2+ elevation in cultured rat hippocampal neurons

This work reports the first demonstration that corticosterone (CORT) has a rapid and transient effect on NMDA receptor‐mediated Ca2+ signaling in cultured rat hippocampal neurons. Using single cell Ca2+ imaging, CORT and agonists of glucocorticoid receptors were observed to modulate the NMDA receptor‐mediated Ca2+ signals in a completely different fashion from pregnenolone sulfate. In the absence of steroids, 100 µm NMDA induced a transient Ca2+ signal that lasted for 30–70 s in 86.1% of the neurons prepared from postnatal rats (3–5 days old). After pre‐treatment with 0.1–100 µm CORT for 10–20 min, NMDA induced extremely prolonged Ca2+ elevation. This prolonged Ca2+ elevation was terminated by the application of MK‐801 and followed by washing out of CORT. The proportion of CORT‐modulated neurons within the NMDA‐responsive cells increased from 25.1 to 95.5% when the concentration of CORT was raised from 0.1 to 50 µm. Substitution of BSA‐conjugated CORT produced essentially the same results. When hippocampal neurons were preincubated with 10 µm cortisol and 1 µm dexamethasone for 20 min, a very prolonged Ca2+ elevation was also observed upon NMDA stimulation. The CORT‐prolonged Ca2+ elevation caused a long‐lasting depolarization of the mitochondrial membrane, as observed with rhodamine 123. In contrast, incubation with 100 µm pregnenolone sulfate did not considerably alter the time duration of NMDA‐induced transient Ca2+ elevation, but caused a significant increase in the peak amplitude of Ca2+ elevation in hippocampal neurons. These results imply that high levels of CORT induce a rapid and non‐genomic prolongation of NMDA receptor‐mediated Ca2+ elevation, probably via putative membrane surface receptors for CORT in the hippocampal neurons.

Three-month stability of delay and probability discounting measures.

Psychopharmacologists are interested in delay and probability discounting because the tendency to discount the value of future and uncertain rewards has been linked with drug dependency. However, relatively little is known about the long-term stability of discounting measures typically studied in clinical psychopharmacology. To evaluate the stability of discounting over a 3-month period, the authors compared points of subjective equality (indifference points) with those collected from the same subjects 3 months earlier. Seven delay periods, ranging from 1 week to 25 years, and 7 probability values, ranging from .95 to .05, were assessed in an undergraduate sample (n=22, delay discounting; n=18, probability discounting). The authors examined both differential stability (stability of individual differences) and absolute stability (stability of the group mean) of delay and probability discounting measures as well as their respective indifference points. The results demonstrate that standard delay and probability discounting parameters (e.g., hyperbolic k and area under the curve) had both differential stability and absolute stability across 3 months. Moreover, most indifference points in the delay and probability discounting tasks demonstrated both differential and absolute stability. All together, these results suggest that delay and probability parameters are stable enough to predict future behavior, such as substance abuse. Additional findings indicated that a hyperbolic function fitted the data better than an exponential function and that delay and probability discounting parameters were not significantly correlated.

Hippocampal cytochrome P450s synthesize brain neurosteroids which are paracrine neuromodulators of synaptic signal transduction

Hippocampal pyramidal neurons and granule neurons of adult male rats are equipped with a complete machinery for the synthesis of pregnenolone, dehydroepiandrosterone, 17beta-estradiol and testosterone as well as their sulfate esters. These brain neurosteroids are synthesized by cytochrome P450s (P450scc, P45017alpha and P450arom) from endogenous cholesterol. Synthesis is acutely dependent on the Ca(2+) influx attendant upon neuron-neuron communication via N-methyl-D-aspartate (NMDA) receptors. Pregnenolone sulfate, estradiol and corticosterone rapidly modulate neuronal signal transduction and the induction of long-term potentiation via NMDA receptors and putative membrane steroid receptors. Brain neurosteroids are therefore promising neuromodulators that may either activate or inactivate neuron-neuron communication, thereby mediating learning and memory in the hippocampus.

Cortisol levels and time-discounting of monetary gain in humans.

This study was conducted to examine the relationship between cortisol levels and preference to a small immediate over a larger delayed monetary reward. The degree of preference to a small immediate reward (a time-discounting rate) was investigated with an economic decision-making task in which each subject made an inter-temporal choice between (a) 10 000 yen available immediately and (b) an equal or larger amount of money after a delay of one year. The time-discounting rate was defined as [the required minimal amount of the delayed monetary gain for (b) to be preferred]-10 000/10 000. Low cortisol levels were shown to associate with a large time-discounting rate, indicating that subjects with low cortisol levels may be impulsive in inter-temporal choice.

Interference and inequality in quantum decision theory

The quantum decision theory is examined in its simplest form of two-condition two-choice setting. A set of inequalities to be satisfied by any quantum conditional probability describing the decision process is derived. Experimental data indicating the breakdown of classical explanations are critically examined with quantum theory using the full set of quantum phases.

Theoretical Frameworks for Neuroeconomics of Intertemporal Choice

Intertemporal choice has drawn attention in behavioral economics, econophysics, and neuroeconomics. Recent studies in mainstream economics have mainly focused on inconsistency in intertemporal choice (dynamic inconsistency); while impulsivity/impatience in intertemporal choice has been extensively studied in behavioral economics of addiction. However, recent advances in neuroeconomic and econophysical studies on intertemporal choice have made it possible to study both impulsivity and inconsistency in intertemporal choice within a unified framework. In this paper I propose the new frameworks for investigations into neuroeconomics of intertemporal choice. The importance of studying neurochemical and neuroendocrinological modulations of intertemporal choice and time-perception (e.g. serotonin, dopamine, cortisol, testosterone, and epinephrine) is emphasized.

Interpersonal trust and social stress-induced cortisol elevation.

A neuroendocrine correlate of interpersonal trust is relatively unknown. We investigated the relationship between an interpersonal trust-related personality (General Trust Scale) and cortisol elevation induced by social stress in 20 men. Spearmans rank order correlation analysis revealed a significant negative correlation between social stress-induced cortisol elevation and General Trust Scale. The present results indicate subjects with higher degrees of interpersonal trust have lower levels of neuroendocrine response to social stress.

Social memory, social stress, and economic behaviors

Social memory plays a pivotal role in social behaviors, from mating behaviors to cooperative behaviors based on reciprocal altruism. More specifically, social/person recognition memory is supposed, by behavioral-economic and game-theoretic analysis, to be required for tit-for-tat like cooperative behaviors to evolve under the N-person iterated prisoners dilemma game condition. Meanwhile, humans are known to show a social stress response during face-to-face social interactions, which might affect economic behaviors. Furthermore, it is known that there are individual differences in a social stress response, which might be reflected in individual differences in various types of economic behaviors, partially via different capacities of social memory. In the present study, we investigated the acute effects of social stress-induced free cortisol (a stress hormone) elevation on hippocampus-dependent social memory by utilizing the Trier social stress test (consisting of a public speech and a mental arithmetic task). We also examine the correlation between an economic behavior-related personality trait (i.e., general trust scale) and social stress-induced cortisol elevations. We found that (1) social stress acutely impairs social memory during social interaction and (2) interpersonal trust reduces social stress response. Together, interpersonal trust may modulate economic behaviors via stress hormones action on social cognition-related brain regions.

Study of the Si(001) clean surface structure using a six-circle surface X-ray diffractometer

Abstract Three-dimensional structure of the Si(001) 2 × 1 surface has been studied using a newly constructed instrument for in-situ characterization of surfaces by X-rays. This instrument consists of a six-circle diffractometer and an ultra-high vacuum chamber capable of molecular beam epitaxy. Measured intensities along four fractional-order reciprocal rods have been analyzed on the basis of an asymmetric dimer model including strain of the substrate over six layers. The bond length and the buckling angle of the dimers are evaluated as (2.37 ± 0.06) A and (20 ± 3)°, respectively.