Holly C. Miller

Can you enhance executive control without glucose? The effects of fructose on problem solving

The consumption of glucose can enhance executive control by increasing blood glucose and providing energy for brain processes. However, a glucose mouth rinse also positively affects executive control in the absence of an effect on blood glucose. This observation suggests that glucose can enhance executive control via another mechanism, perhaps by increasing cortical activation in motivational reward pathways. This hypothesis was examined in the current study by having participants consume fructose, glucose or a placebo 10 minutes before solving word anagrams. Fructose was used because it does not affect blood glucose levels, inhibits cortical responding, and cannot entrain a taste preference post-ingestion. The latter evidences that fructose differs from glucose in its ability to elicit activation in motivational reward pathways. It was observed that consuming fructose and glucose resulted in the resolution of more anagrams than the placebo. These results suggest that at least some of the effects of glucose and fructose on problem solving operate through a common peripheral mechanism that is independent of motivational reward pathways.

Mixed evidence for the potential of non-invasive transcutaneous vagal nerve stimulation to improve the extinction and retention of fear

Extinction memories are fragile and their formation has been proposed to partially rely on vagus nerve activity. We tested whether stimulating the auricular branch of the vagus (transcutaneous VNS; tVNS) accelerates extinction and reduces spontaneous recovery of fear. Forty-two healthy students participated in a 3-day fear conditioning study, where we tested fear acquisition (day 1), fear extinction (day 2) and the retention of the extinction memory (day 3). During extinction, participants were randomly allocated to receive tVNS or sham stimulation concurrently with each CS presentation. During the acquisition and retention phases, all participants received sham stimulation. Indexes of fear included US-expectancy, startle blink EMG and skin conductance responses. Results showed successful acquisition and extinction of fear in all measures. tVNS facilitated the extinction of declarative fear (US expectancy ratings), but did not promote a stronger retention of the declarative extinction memory. No clear effects of tVNS on extinction and retention of extinction were found for the psychophysiological indexes. The present findings provide tentative indications that tVNS could be a promising tool to improve fear extinction and call for larger scale studies to replicate these effects.

Self-regulatory depletion in dogs: insulin release is not necessary for the replenishment of persistence.

It has been hypothesized that self-control is constrained by a limited energy resource that can be depleted through exertion. Once depleted, this resource can be replenished by the consumption or even the taste of glucose. For example, the need to inhibit reduces subsequent persistence at problem solving by humans and dogs, an effect that is not observed when a glucose drink (but not a placebo) is administered following initial inhibition. The mechanism for replenishment by glucose is currently unknown. Energy transfer is not necessary, although insulin secretion may be involved. This possibility was investigated in the current study by having dogs exert self-control (sit-stay) and subsequently giving them (1) glucose that causes the release of insulin, (2) fructose that does not result in the release of insulin nor does it affect glucose levels (but it is a carbohydrate), or (3) a calorie-free drink. Persistence measures indicated that both glucose and fructose replenished canine persistence, whereas the calorie-free drink did not. These results indicate that insulin release is probably not necessary for the replenishment that is presumed to be responsible for the increase in persistence. This article is part of a Special Issue entitled: Canine Behavior.

Guilt by association and honor by association: The role of acquired equivalence

Guilt by association and honor by association are two types of judgments that suggest that a negative or positive quality of a person or object can transfer to another person or object, merely by co-occurrence. Most examples have been demonstrated under conditions of direct associations. Here, we provide experimental evidence of guilt by association and honor by association via indirect associations. We show that participants may treat two individuals alike if they have been separately paired with a common event using an acquired-equivalence paradigm. Our findings suggest that association fallacies can be examined using a paradigm originally developed for research with nonhuman animals and based on a representation mediation account.

The Stroop and Reverse Stroop Effects as Measured by an Interactive Tabletop

An interactive tabletop equipped with RFID technology implemented the Stroop and reverse-Stroop tasks. Participants moved a tangible object into one of four displayed virtual zones, which were identified either by a color border or the name of a color written in black. The correct target zone corresponded either to the color (Stroop) or meaning (reverse Stroop) of a word displayed in congruent or incongruent colored LED lights (e.g., “YELLOW” displayed in yellow or red, respectively). Participants took more time to place the object in a zone, made more errors, and found the task more difficult when the word was lit with an incongruent than congruent color. This interference was influenced by both the types of task and response zone in a way that fits with a dual step processing account. Results also showed that the outcomes of the conflicting information streams might be judged as fun.

Sharing More Than the Sofa: What Dogs Can Teach Us About Human Self-Control

Following an initial act of self-control, human performance on subsequent tasks that also require self-control exertion is impaired. This phenomenon, termed ego depletion, is constrained by beliefs and perceptions in humans. Interestingly, this effect has also been observed in dogs, which arguably do not share similar belief systems. This observation suggests that a common biological mechanism might underlie the phenomenon for both species. It also suggests that we can learn something about human self-control by conducting research with dogs. In this article, we relate findings on the depletion effect in dogs to the different mechanisms that are proposed to explain the effect in humans. Finally, we elaborate on practical implications for working dogs.

A mind cleared by walnut oil: The effects of polyunsaturated and saturated fat on extinction learning

The treatment of anxiety-based psychopathology often hinges upon extinction learning. Research in nutritional neuroscience has observed that the regular consumption of perilla oil (50% alpha-linolenic acid (ALA)) facilitates extinction learning in rats (Yamamoto et al., 1988). However, acute facilitation of extinction learning by oils rich in ALA has not been reported for rats or humans, though the acute consumption of rapeseed oil (10% ALA) has been observed to improve cognitive processing speed in humans (Jones, Sünram-Lea, & Wesnes, 2012). For this reason, the present laboratory work examined the effects of adding walnut oil (12% ALA) to a chocolate milkshake on the acquisition, generalization, and extinction of a fear-based prediction in young adults. It compared performance between subjects. The other participants consumed a similar milkshake with either an equicaloric amount of cream (saturated fat), or with no added fat (control). Acquisition and generalization of the fear-based prediction were similar for all groups. However, those who consumed walnut oil extinguished most rapidly and profoundly. Implications for extinction learning are discussed.

There is no sweet escape from social pain: Glucose does not attenuate the effects of ostracism

Ostracism causes social pain and is known to activate regions of the brain that are involved in the representation of physical pain. Previous research has observed that acetominophen (a common pain reliever) can reduce the pain of exclusion. The taste and consumption of glucose can also relieve physical pain, and the purpose of the current study was to examine whether it might also reduce the negative emotional effects of ostracism. In an appropriately powered experiment, participants were given 25g of glucose or a sucralose placebo before being ostracized while playing Cyberball. Strong effects of ostracism were observed, however, there was no effect of glucose on immediate or delayed self-reported needs or mood. These results are discussed in reference to the possibility that social pain is unlike physical pain since the latter is affected by glucose, which is believed to lessen pain by increasing endogenous opioid activity.

Spatial integration of boundaries in a 3D virtual environment

Prior research, using two- and three-dimensional environments, has found that when both human and nonhuman animals independently acquire two associations between landmarks with a common landmark (e.g., LM1-LM2 and LM2-LM3), each with its own spatial relationship, they behave as if the two unique LMs have a known spatial relationship despite their never having been paired. Seemingly, they have integrated the two associations to create a third association with its own spatial relationship (LM1-LM3). Using sensory preconditioning (Experiment 1) and second-order conditioning (Experiment 2) procedures, we found that human participants integrated information about the boundaries of pathways to locate a goal within a three-dimensional virtual environment in the absence of any relevant landmarks. Spatial integration depended on the participant experiencing a common boundary feature with which to link the pathways. These results suggest that the principles of associative learning also apply to the boundaries of an environment.