Brain Cells in the Avian ‘Prefrontal Cortex’ Code for Features of Slot-Machine-Like Gambling

Slot machines are the most common and addictive form of gambling. In the current study, we recorded from single neurons in the ‘prefrontal cortex’ of pigeons while they played a slot-machine-like task. We identified four categories of neurons that coded for different aspects of our slot-machine-like task. Reward-Proximity neurons showed a linear increase in activity as the opportunity for a reward drew near. I-Won neurons fired only when the fourth stimulus of a winning (four-of-a-kind) combination was displayed. I-Lost neurons changed their firing rate at the presentation of the first nonidentical stimulus, that is, when it was apparent that no reward was forthcoming. Finally, Near-Miss neurons also changed their activity the moment it was recognized that a reward was no longer available, but more importantly, the activity level was related to whether the trial contained one, two, or three identical stimuli prior to the display of the nonidentical stimulus. These findings not only add to recent neurophysiological research employing simulated gambling paradigms, but also add to research addressing the functional correspondence between the avian NCL and primate PFC

Histology.

<p>A) Lateral view of the pigeon brain. The nidopallium caudolateral (NCL) is shaded in red. The black line represents the intended electrode trajectory. B) Top view of the pigeon brain. The dot represents the intended position of the electrode entry point in NCL. C) Histological reconstruction of the electrode tracks for the five pigeons. The black lines represent the electrode track. All tracks were within the boundaries of the NCL. A: arcopallium; Ad: arcopallium dorsale; Av: arcopallium mediale; APH: area parahippocampalis; DA: tractus dorso-arcopallialis; Hp: Hippocampus; HV: mesopallium; NC: nidopallium caudale; SGF: stratum griseum et fibrosum superficiale; V: ventricle.</p

I-Lost Neuron.

<p>Response profile of an I-Lost neuron to each of the four tumblers on nonrewarded trials. The activity drops the moment it becomes apparent that no reward will be delivered. The period during which neural responses were measured was 300 msec, from 100–400 msec after a peck to the stimulus displayed on each tumbler. The binwidth is 25 msec.</p

Near-Miss Neuron.

<p>Response profile of Near-Miss to the first nonidentical stimulus after one (left), two (center), or three (right) identical stimuli appearing on the tumblers. In the case of this neuron, the activity level increases as a function of the number of previous identical stimuli. The period during which neural responses were measured was 300 msec, from 100-400 msec after a peck to the stimulus displayed on each tumbler. The binwidth is 25 msec.</p

Reward-Proximity Neuron.

<p>Response profile of a Reward-Proximity neuron to each of the four tumblers on rewarded trials. The neuron shows a steady increase in firing on rewarded trials as the opportunity of a reward draws near. The period during which neural responses were measured was 300 msec, from 100–400 msec after a peck to the stimulus displayed on each tumbler. The binwidth is 25 msec. Displayed is just one of the four possible winning combinations.</p

I-Won Neuron.

<p>Response profile of an I-Won neuron to each of the four tumblers on rewarded trials. The activity on the first three tumblers is no different to baseline activity, but activity to the fourth identical stimulus results in an increase in activity. The period during which neural responses were measured was 300 msec, from 100–400 msec after a peck to the stimulus displayed on each tumbler. The binwidth is 25 msec. Displayed is just one of the four possible winning combinations.</p