In a lab at Stanford University, a mouse is showing signs of depression. For around 10 weeks, it has experienced a series of irritations, from bouts without food or water, to erratic sleep patterns. Now, its motivation is low—when picked up by the tail, it makes few attempts to escape, and it doesn’t try to explore new spaces. It’s also less willing to sip from a sugary liquid– a sign that it gets less pleasure from normally pleasurable activities. It is never easy to assess the mental health of an animal, but this mouse is clearly showing some of the classic symptoms of depression.
But not for long.
Earlier, Kay Tye and Julie Mirzabekov altered the mouse so that a flash of light can activate a small part of its brain—the ventral tegmental area (VTA), near the bottom of the brain and close to the midline. A burst of light, and the mouse’s behaviour changes almost instantly. It struggles when held aloft, it explores open areas, and it regains its sweet tooth. A burst of light, and its symptoms disappear.
But on the other side of the country, at the Mount Sinai School of Medicine, Dipesh Chaudhury and Jessica Walsh are doing the same thing to completely different effect. Their mice have been altered in a similar way, so that light can also switch on their VTA neurons. But these rodents have endured a shorter but more intense form of stress—10 days of being placed in cages with dominant, aggressive rivals. Because of the resulting attacks, some of them have developed depressive symptoms. Others are more resilient. But when Chaudhury and Walsh flashed the VTAs of these mice, resilient individuals transformed into susceptible ones.
Both studies used the same methods to trigger neurons in the same part of the brain… and got completely different effects. In Tye and Mirzabekov’s experiment, depressed mice resumed their normal behaviour. In Chaudhury and Walsh’s study, the resilient mice showed more depressed symptoms.