Pavlov and appetite

Biological Prescience: The Role of Anticipation in Organismal Processes

Anticipation is the act of using information about the past and present to make predictions about future scenarios. As a concept, it is predominantly associated with the psychology of the human mind; however, there is accumulating evidence that diverse taxa without complex neural systems, and even biochemical networks themselves, can respond to perceived future conditions. Although anticipatory processes, such as circadian rhythms, stress priming, and cephalic responses, have been extensively studied over the last three centuries, newer research on anticipatory genetic networks in microbial species shows that anticipatory processes are widespread, evolutionarily old, and not simply reserved for neurological complex organisms. Overall, data suggest that anticipatory responses represent a unique type of biological processes that can be distinguished based on their organizational properties and mechanisms. Unfortunately, an empirically based biologically explicit framework for describing anticipatory processes does not currently exist. This review attempts to fill this void by discussing the existing examples of anticipatory processes in non-cognitive organisms, providing potential criteria for defining anticipatory processes, as well as their putative mechanisms, and drawing attention to the often-overlooked role of anticipation in the evolution of physiological systems. Ultimately, a case is made for incorporating an anticipatory framework into the existing physiological paradigm to advance our understanding of complex biological processes.

Eating behavior as a new frontier in memory research

The study of memory is commonly associated with neuroscience, aging, education, and eyewitness testimony. Here we discuss how eating behavior is also heavily intertwined-and yet considerably understudied in its relation to memory processes. Both are influenced by similar neuroendocrine signals (e.g., leptin and ghrelin) and are dependent on hippocampal functions. While learning processes have long been implicated in influencing eating behavior, recent research has shown how memory of recent eating modulates future consumption. In humans, obesity is associated with impaired memory performance, and in rodents, dietary-induced obesity causes rapid decrements to memory. Lesions to the hippocampus disrupt memory but also induce obesity, highlighting a cyclic relationship between obesity and memory impairment. Enhancing memory of eating has been shown to reduce future eating and yet, little is known about what influences memory of eating or how memory of eating differs from memory for other behaviors. We discuss recent advancements in these areas and highlight fruitful research pursuits afforded by combining the study of memory with the study of eating behavior.

The kingdom of dogs: Understanding Pavlov’s experiments as human–animal relationships

The growth of Human–Animal Studies, multi-species, and posthuman scholarship reflects an “animal turn” offering important theoretical, ethical, and methodological challenges to humanities, science, and social science disciplines, though psychology, in particular, has been slow to engage with these developments. This article is the first to apply the conceptual lens of the “animal turn” to Pavlov’s experiments with dogs. It is unique in applying in particular the work of feminist cultural theorist Donna Haraway, to radically reframe the human–animal relationship at the core of these landmark experiments. This original portrait is contrasted with contemporary retellings of those experiments which ignore or are indifferent to the complexities of that relationship. Paying attention to nonhuman others that constitute animal experimentation in psychology, historically, today, and in retellings, is argued to be a vitally important step for psychology today. The analysis provided constitutes a distinctive, radical shift in the way psychology might approach the lives of nonhuman animals, in its own past and present, with far-reaching implications for the future development of psychology.

Food odors trigger an endocrine response that affects food ingestion and metabolism

Food odors stimulate appetite and innate food-seeking behavior in hungry animals. The smell of food also induces salivation and release of gastric acid and insulin. Conversely, sustained odor exposure may induce satiation. We demonstrate novel effects of food odors on food ingestion, metabolism and endocrine signaling in Drosophila melanogaster. Acute exposure to attractive vinegar odor triggers a rapid and transient increase in circulating glucose, and a rapid upregulation of genes encoding the glucagon-like hormone adipokinetic hormone (AKH), four insulin-like peptides (DILPs) and some target genes in peripheral tissues. Sustained exposure to food odors, however, decreases food intake. Hunger-induced strengthening of synaptic signaling from olfactory sensory neurons (OSNs) to brain neurons increases food-seeking behavior, and conversely fed flies display reduced food odor sensitivity and feeding. We show that increasing the strength of OSN signaling chronically by genetic manipulation of local peptide neuromodulation reduces feeding, elevates carbohydrates and diminishes lipids. Furthermore, constitutively strengthened odor sensitivity altered gene transcripts for AKH, DILPs and some of their targets. Thus, we show that food odor can induce a transient anticipatory endocrine response, and that boosted sensitivity to this odor affects food intake, as well as metabolism and hormonal signaling.

Anticipatory physiological regulation in feeding biology: cephalic phase responses

Anticipatory physiological regulation is an adaptive strategy that enables animals to respond faster to physiologic and metabolic challenges. The cephalic phase responses are anticipatory responses that prepare animals to digest, absorb, and metabolize nutrients. They enable the sensory aspects of the food to interact with the metabolic state of the animal to influence feeding behavior. The anticipatory digestive secretions and metabolic adjustments in response to food cues are key adaptations that affect digestive and metabolic efficiency and aid in controlling the resulting elevation of metabolic fuels in the blood. Cephalic phase responses enable digestion, metabolism, and appetite to be regulated in a coordinated fashion. These responses have significant effects on meal size. For example, if the cephalic phase insulin response is blocked the result is poor glucose control and smaller meals. Cephalic phase responses also are linked to motivation to feed, and may play a more direct role in regulating meal size beyond the permissive one of ameliorating negative consequences of feeding. For example, the orexigenic peptide ghrelin appears to display a cephalic phase response, rising before expected meal times. This anticipatory ghrelin response increases appetite; interestingly it also enhances fat absorption, linking appetite with digestion and metabolism.

Pavlov and integrative physiology

Ivan Petrovich Pavlov was the first physiologist to win the Nobel Prize. The Prize was given in 1904 for his research on the neural control of salivary, gastric, and pancreatic secretion. A major reason for the success and novelty of his research was the use of unanesthetized dogs surgically prepared with chronic fistulas or gastric pouches that permitted repeated experiments in the same animal for months. Pavlov invented this chronic method because of the limitations he perceived in the use of acute anesthetized animals for investigating physiological systems. By introducing the chronic method and by showing its experimental advantages, Pavlov founded modern integrative physiology. This paper reviews Pavlov's journey from his birthplace in a provincial village in Russia to Stockholm to receive the Prize. It begins with childhood influences, describes his training and mentors, summarizes the major points of his research by reviewing his book Lectures on the Work of the Digestive Glands, and discusses his views on the relationship between physiology and medicine.