While the role of motivation on the performance of behavioural tasks has been known for more than a century – thanks to the work of psychologists Robert Yerkes and John Dilligham Dodson – its precise effect on the brain remains unclear.
A team from the University of Geneva (UNIGE), in collaboration with the EPFL, has revealed how motivation alters the neural circuits responsible for sensory perception preceding decision-making in mice.
These results, featured in the journal Neuron, open up new perspectives in learning methods.
Going to work early in the morning, choosing a restaurant at lunchtime: many of our decisions are motivated by needs, such as earning a living or satisfying our hunger.
The laboratory of Sami El-Boustani, Assistant Professor in the Department of Basic Neurosciences at the Faculty of Medicine of the UNIGE and recipient of an Eccellenza fellowship (SNSF), is studying the neural circuits involved in decision-making. In recent work, carried out in collaboration with Professor Carl Petersen’s team at EPFL, his lab has studied the role played by a specific internal state – motivation – in perception and decision-making.
For more than a century it has been known that a relationship between motivation and performance exists thanks to the work of American psychologists Robert Yerkes and John Dilligham Dodson. Too much or too little motivation is detrimental to performance. However, the way in which this impacts our neural circuits remains unclear.
The research team developed a behavioral paradigm involving mice in a controlled water consumption regime. They first trained these rodents to respond to tactile stimuli via two whiskers (A and B) and to produce an action – licking a spout – only for whisker A in order to obtain a drop of water.
Following this training, these mice reacted mainly to the stimulation of whisker A, thus indicating their ability to discriminate between these two sensations. Finally, the researchers conducted these experiments at decreasing levels of thirst in order to vary the motivation of the rodents to participate in the task.
State of hyper-motivation blurs sensory information
In a state of great thirst – therefore of great motivation – rodents performed poorly. They licked the spout indiscriminately, without distinguishing between the whiskers stimulated.
In contrast, in a state of moderate thirst, the choice of their action became optimal. They mainly licked the spout when whisker A was stimulated. Finally, when they were not very thirsty, their performance in the task dropped again.
By observing the activity of neuronal populations responsible for perceptual decision-making in these mice, the researchers discovered that neurons in these circuits were flooded with electrical signals when mice were hyper-motivated. Conversely, in a state of low-motivation, the signals were too weak.
‘‘Hyper-motivation leads to strong stimulation of cortical neurons, which causes a loss of precision in the perception of tactile stimuli,’’ says Giulio Matteucci, a Postdoctoral Fellow in Sami El-Boustani’s laboratory and the study’s first author.
In contrast, in the low-motivation state, the accuracy of the sensory information was recovered, but the strength of the signal was too low for it to be transferred correctly. As a result, the perception of the stimuli was also impaired.
A new understanding of learning
These results open up new perspectives. They provide a possible neural basis for the Yerkes-Dodson Law.
‘‘They also reveal that the level of motivation does not only impact decision-making but also the perception of sensory information, which leads to the decision’’, explains Carl Petersen, Full Professor at the Brain Mind Institute of EPFL and co-senior author in the study.
This work also suggests that it is necessary to decouple acquisition and expression of new knowledge.
‘‘We observed that mice understood the rule very quickly but could only express this learning much later, depending on an altered perception linked to their level of motivation.’’
This unraveling of the role of motivation in learning opens the way to new adaptive methods that aim to maintain an optimal level of motivation during learning.
The Impact of Motivational States
There exist some indirect hints that the motives underlying wishful thinking have an impact on visual perception. Recent work focusing on more biologically oriented motivational states shows that they influence the perception of visual stimuli.
For example, Changizi and Hall (2001) demonstrated that participants who were thirsty perceived more transparency in ambiguous visual stimuli than did those who were not thirsty, presumably because transpar- ency is a characteristic associated with water.
Women during periods of high fertility were faster to categorize male photographs than female ones by gender, relative to those not in such a fertile state (Macrae, Alnwick, Milne, & Schloerscheidt, 2002). It is important that the same comparative enhancement was not present for women taking a contraceptive pill or those who were pregnant (Johnston, Arden, Macrae, & Grace, 2003).
Both of these exam- ples suggest an enhanced perceptual sensitivity for features in visual stimuli that are relevant to biological drives or desires.
But would a drive toward wishful thinking similarly influence perception? In a sense, this question is a revisiting and a reopening of one of the focal issues of the New Look approach to perception that arose in psychology during the 1940s and 1950s (Bruner & Minturn, 1955).
According to New Look theorists, perception was an active and constructive process influenced by many top-down factors. One class of such factors was the needs and values of the perceiver. For example, Bruner and Goodman (1947) asked children in diverse social economic conditions to estimate the size of monetary coins by manipulating the diameter of a beam of light.
Poorer children, for whom the value of money was greater, overestimated the size of the coins compared with more affluent children, who were presumed to place less value on the same coins. In studies of perceptual defense, New Look theorists con- cluded that participants inhibited the recognition of threatening stimuli, such as troubling words (Postman, Bruner, & McGinnies, 1948).
These initial demonstrations of motivational influences on per- ception were met with much enthusiasm, which was then followed by withering criticism. To be sure, much of what the New Look theorists proposed has lasted through today and informs contem- porary cognitive and perceptual psychology in fundamental ways. Psychologists uniformly agree with the New Look tenet that much of cognition happens nonconsciously, that is, outside a person’s awareness, monitoring, or control (Greenwald, 1992; Wegner & Bargh, 1998).
Many modern textbooks describe the New Look proposal that perception is filtered: that the representation of the environment that people have in consciousness has omitted a good deal of information that is actually in the environment (Allport, 1989; Miller, 1987). Similarly, perception of an object is impor- tantly influenced by the perceiver’s expectations as well as the context surrounding that object (Biederman, Mezzanotte, & Rabi- nowitz, 1982; Boyce & Pollatsek, 1992; Li & Warren, 2004; Long & Toppino, 2004).
However, the specific New Look assertion that motivational states influence perception did not achieve the same stature and longevity as these other insights. It, instead, ran aground in the 1950s on the rocky shoals of methodological difficulties and theoretical controversies (Eriksen, 1958, 1962; Eriksen & Browne, 1956; Goldiamond, 1958; Prentice, 1958; Wohlwill, 1966).
Critics pointed out that poorer children might misjudge the size of coins because they were not as familiar with them, or that their misjudgments might involve problems of memory rather than perception (McCurdy, 1956). Critics also noted in studies of perceptual de- fense that participants might have taken longer to report troubling words not because it took them longer to perceive them but rather because it took longer to get over the surprise of seeing them or the embarrassment of saying them (Erdelyi, 1974, 1985). Others la- mented that the relative unfamiliarity of threatening words, and not their motivational punch, was the key ingredient that slowed participants’ recognition responses (Adkins, 1956; Howes & So- lomon, 1950).
As such, the influence of motivational states on perception was never firmly established. And as the 1950s closed the study of the relation between motivational states and perception, this pursuit fell by the wayside and ceased to have the major impact—if any at all— enjoyed by other insights from the New Look tradition (Dun- ning, 2001; Erdelyi, 1974; Gilbert, 1998; Jones, 1985; Nisbett &
Ross, 1980).
reference link : DOI: 10.1037/0022-3514.91.4.612
Original Research: Open access.
“Cortical sensory processing across motivational states during goal-directed behavior” by Sami El-Boustani et al. Neuron
