I came across a recently published study that I simply MUST share and comment on:
“Unexpected rewards induce dopamine-dependent positive emotion-like state changes in bumblebees.”
Wait–emotions and bumblebees in the same title?!
When I worked with bumblebees I certainly saw what could be interpreted as emotion-like behaviour. For instance, I would allow bumblebees to forage for nectar from articifical flowers I had in a flight cage (a screened-in, gazebo-like structure). The bumblebee “nest,” which was a wooden or plastic box, was connected to the flight cage via a tunnel with a gate I could control. I was literally the “gatekeeper” for which bumblebees could enter the flight cage. Soon I was able to identify which bumblebees were the keen foragers: they would race down the tunnel, fly directly to the flowers, eat, fly directly back to the tunnel, and scurry home. They were all business. If I saw these bees come out of the nest and I put the gate down so they couldn’t enter the flight cage, they would buzz and buzz and literally hop up and down repeatedly right in front of the gate until I opened it.
These bumblebees were certainly showing something. Frustration? Excitement? Murderous rage?
But these are human interpretations of behaviour. What were the bumblebees experiencing, if anything? That’s the key question.
Let’s have a look at the published study. What did they do to show that bumblebees exhibit emotion-like behaviour?
It’s pretty clever.
All of the experiments with the bumblebees were based on this one, dare I say, fact: When humans eat something sweet, they experience positive emotions. (Mmmm…pumpkin pie!)
Before bumblebees were given a test, the researchers gave them a bit of sugar water. Would the bumblebees show behaviour that is consistent with a positive emotion state?
(Another thing to keep in mind: Positive emotion states often result in biased decision-making: there is a tendency (for example, after eating a piece of pumpkin pie) to respond positively to ambiguous stimuli, and to react less negatively to aversive things.)
In the first experiment, bumblebees were trained to land on blue artificial flowers but not green ones. Then they were given an ambiguous situation where they were presented with a flower that was blue-green in colour. Before the blue-green test some bumblebees were given a droplet of sugar water. The bumblebees who got the sugar water took less time to land on the blue-green flower compared to bumblebees who did not get any “sweet snack.” In other words, the sweet snack lead to a positive response to an ambiguous stimuli, which is consistent with positive emotions.
(I should note that the researchers did some extra tests to rule out the possibilities that the sweet snack simply made the bees “expect” more sugar water, or made the bees more excited or active, and were thus more likely to explore the new blue-green colour. I’ll save you the gory details. But they are convincing.)
In another test, bumblebees were trained to drink from a feeder and then they experienced a simulated predator attack (what?!): a sponge pressing gently down on the bee, restraining it from moving for 3 seconds. Before the “predator attack,” some bumblebees got a droplet of sugar water. The bumblebees who received the sugar water took less time to resume foraging from the feeder after the “predator attack” compared to bumblebees who received no sugar water. So, the sweet snack was associated with the bumblebees reacting less negatively to the aversive event, which is consistent with positive emotions.
Finally, the last experiment is where things are really cool. The title of the research study has the word “dopamine” in it, which refers to a chemical (neurotransmitter) in the brain that is involved in the reward system. In other words, dopamine is one of the key neurotransmitters that is active in your brain (and in other species’s brains) when you are experiencing something positive. (Like pumpkin pie!)
The researchers subjected some new bumblebees to the “predator attack” experiment. This time all bumblebees received a drop of sugar water before the attack. Some bumblebees, though, were treated with a chemical that blocks dopamine. (There isn’t much detail in plain English about what this treatment was exactly, other than it was “topical.” So I guess it was some kind of liquid/substance that they rubbed onto the bees’ bodies?? Or sprayed on them??)
Anyway, the bumblebees that were treated with the dopamine-blocker took the longest to resume foraging after the predator attack. Thus, the dopamine-blocker prevented a positive emotion-state, which resulted in the bees taking longer to recover after the predator attack.
The researchers also repeated the blue-green test with new bumblebees: this time all bumblebees received sugar water before the test, but some bees got the dopamine blocker. The bees with the dopamine blocker took longer to land on the blue-green flower. Less dopamine, less positive emotion-state, less likely to respond positively to ambiguous things.
So, in a nutshell:
- Like humans, giving bumblebees a sweet treat can result in behaviour that is associated with a positive emotion-state: a bias to respond positively to ambiguous things, and an ability to recover more quickly after aversive events.
- The sweet treat does not simply give the bees more energy, or simply make them behave in a way that suggests they expect more treats.
- Blocking a brain chemical in bumblebees that is involved in positive emotion states also blocks behaviour that is associated with positive emotion states.
Whew! That was a long post. Probably the longest post I’ve written about a research study. But emotions are complex, especially when it comes to other animals. Especially invertebrates!
Are you convinced that bumblebees have emotion-like states? I think it’s pretty convincing.
But no experiment is perfect.
Like I mentioned earlier, we can’t know what the bumblebees experienced. Did they experience a mental state that is associated with positive emotions? Were they in sugar-water-bliss? Or did the sugar water have no mental effect at all, and only altered their observable behaviour?
Something to ponder about over a piece of pumpkin pie.
Perry, C. J., Baciadonna, L., & Chittka, L. (2016). Unexpected rewards induce dopamine-dependent positive emotion-like state changes in bumblebees. Science, 353(6307), 1529-1531.