This program offers the hope that internal states hidden to behavioral observation can be monitored by neuroscientific means and, particularly in laboratory animals, can be manipulated so as to support causal inferences. However, the neuroeconomist draws particular inspiration from the striking successes achieved in fields such as molecular biology, where our understanding of function has been expanded profoundly by discoveries about structure and mechanism. A neuroeconomic perspective has informed several different experimental paradigms for the study of decision making in non-human animals Glimcher, ; Glimcher et al.
One of these entails pursuit of rewarding electrical brain stimulation Shizgal, In the following sections, I describe a variant of this paradigm Breton et al. At the end of this essay, I sketch a path from this particular way of studying animal decision making to broader issues in neuroeconomics.
Rats, and many other animals, will work vigorously to trigger electrical stimulation of brain sites arrayed along the neuraxis, from rostral regions of prefrontal cortex to the nucleus of the solitary tract in the caudal brainstem. Although the stimulation makes no known contribution to the satisfaction of physiological needs, the animals act as if BSR were highly beneficial, and they will work to the point of exhaustion in order to procure the stimulation.
Adaptive allocation of scarce behavioral resources requires that benefits and costs be assessed and combined so as to provide a result that can serve as a proxy for enhancement of fitness. The electrical stimulation that is so ardently pursued appears to inject a meaningful signal into neural circuitry involved in computing the value of goal objects and activities.
For example, the rewarding effect produced by electrical stimulation of the medial forebrain bundle MFB can compete with, summate with, and substitute for the rewarding effects produced by natural goal objects, such as sucrose and saline solutions Green and Rachlin, ; Conover and Shizgal, ; Conover et al. This implies that the artificial stimulation and the gustatory stimuli share some common attribute that permits combinatorial operations and ultimate evaluation in a common currency.
My coworkers and I have likened the intensity dimension of BSR to the dimension along which the reward arising from a tastant varies as a function of its concentration Conover and Shizgal, ; Hernandez et al. On this view, a rat that works harder for an intense electrical reward than for a weaker one is like a forager that pursues a fully ripe fruit more ardently than a partially ripe one. Both are relinquishing a goal they would have sought under other circumstances for a different goal that surpasses it in value.
Viewed in this way, the subjective intensity dimension is fundamental to economic decision making, as defined in the broad manner advocated here. In many experiments on intracranial self-stimulation ICSS , the cost column of the ledger is manipulated by altering the contingency between delivery of the rewarding stimulation and a response, such as lever pressing. One of our schedules imposes a well controlled opportunity cost on the electrical reward Breton et al.
The opportunity cost is the value of the alternate activities that must be forgone to obtain the experimenter-controlled reward. In behavioral ecology, handling-time refers to the period during which a prey item is first rendered edible, e. To paraphrase Robbins, the conditions of the cumulative handling-time schedule require that if the rat chooses to engage in one activity, such as holding down the lever, it must relinquish others, such as grooming, exploring, or resting, which, in different circumstances e.
Like stimulation strength, price acts as an economic variable, as defined in the broad manner advocated here. The key to making time a scarce resource is to ensure the exclusivity of the different activities in which the rat might engage. An exception illustrates the rule.
In an early test of our cumulative handling-time schedule, a rat was seen to turn its back to the lever, hold it down with its shoulder blades, and simultaneously groom its face. By repositioning the lever, we were able to dissuade this ingenious fellow from defeating our intentions, and none of our rats have been seen since to adopt such a sly means of rendering their time less scarce. Traditional schedules of reinforcement Ferster and Skinner, do not enforce stringent time allocation. Ratio schedules do control effort costs, but they leave open the option of trading off opportunity costs against the additional effort entailed in responding at a higher cadence.
In contrast, the cumulative handling-time schedule enforces a strict partition of time between work and leisure. We define an experimental trial as a time interval during which the price and strength of the electrical reward are held constant. The trial duration is made proportional to the price, and thus, a rat that works incessantly will accumulate a fixed number of rewards per trial.
When the price of BSR is low, the rat forgoes leisure activities and spends almost all its time holding down the lever to earn electrical rewards. As the price is increased, the rat re-allocates the scarce resource its time , engaging more in leisure activities and less in work. Thus, the higher the frequency at which pulses are delivered during a train, the more intense the neural response, and the more time is allocated to pursuit of BSR.
Sample data Hernandez et al. A time allocation to pursuit of trains of different opportunity cost with reward strength held constant; B time allocation to pursuit of trains of different strength with opportunity cost held constant; C time allocation to pursuit of trains with inversely correlated strength and opportunity cost strong trains are cheap, weak ones are expensive , plotted as function of opportunity cost; D time allocation to pursuit of trains with inversely correlated strength and opportunity cost strong trains are cheap, weak ones are expensive , plotted as function of strength.
To obtain this map, the reward mountain is sectioned horizontally at regular intervals and the resulting profiles plotted as black lines; the gray level represents the altitude time allocation. A Scatter plot of data means along the with surface fitted to the data; B contour plot of the fitted surface and the sampled pulse frequencies and prices. The solid red line represents the position parameter of the intensity-growth function: the pulse frequency that produces a reward of half-maximal intensity. This parameter determines the position of the three-dimensional structure along the pulse frequency axis.
The solid blue line represents the price at which time allocated to pursuit of a maximal reward falls half-way between its minimal and maximal values; this parameter determines the position of the three-dimensional structure along the price axis. Each component is assigned a specific role in processing the signal injected by the electrode and in translating it into an observable behavioral output. The correspondence of the fitted surface to the data hints that it can. Insofar as the model specifies psychological processes involved in economic decisions, the model is positioned within the behavioral-economic tradition, and insofar as at least some of its components are couched in terms of neural activity, it is also has a neuroeconomic flavor.
The derivation of the expressions and their empirical basis is provided in the cited paper. The elements of this vector are subjective values. Thus, the top and bottom elements are simply the subjective mapping of stimulation strength and opportunity cost. The remaining two elements represent the subjective estimate of the probability of receiving a reward upon satisfaction of the response requirement and the physical exertion required to hold down the lever. Note the analogy between this model and prospect theory. In both cases, non-linear functions map objective economic variables into subjective ones, and the results are combined in scalar fashion.
gspiii.crabdance.com/presentando-mi-candidatura-a-ser-vivo.php In both cases, the form and parameters of the mapping functions matter. To translate the payoffs obtained by scalar combination of the quantities in the memory vector into observable behavior, an adaptation Hernandez et al. Several stages of processing are shown, including one of the four psychophysical functions that generate the values stored in the memory vector. The schema at the left represents the inference that over a wide range of frequencies, each pulse triggers a volley of action potentials in the directly stimulated neurons responsible for the rewarding effect Gallistel, ; Gallistel et al.
The synaptic output of these neurons is integrated spatially and temporally and transformed by an intensity-growth function. In accord with experimental data Leon and Gallistel, ; Simmons and Gallistel, ; Arvanitogiannis and Shizgal, ; Hernandez et al. The scaled output of the intensity-growth function is passed through a peak detector en route to memory: it is the maximum intensity achieved that is recorded Sonnenschein et al.
Ongoing research Solomon et al. The subjective probability and effort—cost functions have yet to be described. The price is the cumulative time the rat must hold down the lever in order to earn a reward. Thus, from the perspective of the Mazur model, the price is couched as a delay to reward receipt, and the subjective-price is inversely related to the discounted value.
The value of the reward at zero delay has been set arbitrarily to one. Alternative models of the subjective-price function are under ongoing investigation Solomon et al. The non-linear form of this function makes it possible to discern in what direction the mountain surface described by these contours has been displaced by experimental manipulation of the reward circuitry. Interventions in the early stages, prior to the output of the intensity-growth function, displace the mountain along the axis representing the strength of the rewarding stimulation pink surface.
In contrast, interventions in later stages displace the mountain along the axis representing the cost of the rewarding stimulation blue surface. Consequently, the reward mountain can be used to narrow down the stages of processing at which manipulations such as drug administration, lesions, or physiological deprivation act to alter reward seeking. Inferring the stages of processes responsible for shifts of the mountain.
A The mountain model.
An Essay on the Nature and Significance of Economic Science by Lionel Robbins first appeared in as an outstanding English-language statement of the. Other articles where Essay on the Nature and Significance of Economic Science is discussed: Lionel Charles Robbins, Baron Robbins: His Essay on the Nature.
Experimental manipulations that act on the early stages of processing, prior to the output of the intensity-growth function, shift the three-dimensional structure along the pulse frequency axis B whereas manipulations that act on later stages produce shifts along the price axis C. Thus, measuring the effects of such manipulations on the position of the three-dimensional structure constrains the stages of processing responsible for the behavioral effects of the manipulations.
On this basis, the enhancement of reward seeking produced by cocaine Hernandez et al.
The correspondence of the fitted surface to the data hints that it can. One favorable sign is the increased focus on replicability of empirical work in economics. The key to making time a scarce resource is to ensure the exclusivity of the different activities in which the rat might engage. The main objectives of the RBJA include:. Sipson , Middlesex.
In early work on the role of dopamine neurons in BSR, the changes in reward pursuit produced by manipulation of dopaminergic neurotransmission were attributed to alterations in reward intensity Crow, ; Esposito et al. However, cocaine, a drug that boosts dopaminergic neurotransmission, displaces the 3D reward mountain rightward along the price axis Hernandez et al.
This links the drug-induced change in dopamine signaling to a later stage of processing than was originally proposed, one beyond the output of the intensity-growth function.