APPETITE

The mechanisms that control appetite and feeding behaviour

The mechanisms that control appetite and feeding behaviour

Introduction

Eating is a behavioural act carried out through the voluntary skeletal musculature, it is often believed that eating is invariably under voluntary conscious control. Despite the fact that eating is an action open to awareness by the individual, it cannot be claimed that processes that control the expression of eating habits are necessarily explicit. Furthermore, introspective accounts of explicit processes are often subject to misinterpretation and cross-contamination (Berridge, 1996; Booth, 1987).

Brain involvement

As neuroimaging technologies, such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and electroencephalography (EEG), have become more readily available, researchers have produced an upsurge of studies comparing the brain responses of normal weight and obese individuals to a variety of stimuli and physiological states. These new technologies have great potential to supplement existing literature on behavioral differences between individuals within these weight categories.

An illustration of the potential of neuroimaging to clarify behavioral studies can be found in literature comparing obese and normal weight individuals on measures of appetite and food intake. There have been hundreds of behavioral studies comparing normal weight and overweight individuals on these variables during the past 40 years, but these studies have often produced conflicting and contradictory results.

Neuroimaging research that has compared brain regions associated with eating behavior in obese and normal weight individuals, by contrast, has shown much more consistent differences between these groups. The fact that there is more consistency in findings in neuroimaging compared to behavioral studies suggests that investigating the reasons for this difference will yield valuable insights into both neurophysiological and behavioral processes that might contribute to obesity.

Although neuroimaging technologies have identified a variety of brain areas in obese and normal weight individuals that are differentially activated in response to various manipulations, such differences cannot be assumed to reveal the brain processes that underlie vulnerability to chronic positive energy balance and weight gain.

That is, because the development of obesity could both produce and result from characteristic patterns of resting and stimulated brain activity, the documentation of such differences cannot provide definitive information about brain -based predispositions that may underlie the development of obesity. Furthermore, past research has clearly shown that there is tremendous variation within normal weight and obese groups on variables that may be relevant to the development of obesity.

Such variables include negative affect, responsiveness to internal and external cues, food craving, restrained eating and disinhibition and binge eating. It is important to understand the neural underpinnings of variables such as these in both normal weight and overweight populations, albeit for somewhat different reasons.

Hormonal factors associated with appetite control

An individual may have awareness of the act of eating per se whilst remaining unaware of the processes that determine the expression of appetite and the pattern of eating. It is, of course, obvious that a person cannot be aware of the (implicit) changes in neuropeptides, hormones or other physiological processes that help to determine the initiation, termination and ...