Flexible Inhibitory Control of Visually Evoked Defensive Behavior
Tis the season for ghosts and ghouls and things that go bump in the night. Fear is a drug many of us seek out whether it’s a scary slasher horror flick fueled by the slow meandering of Michael Meyers or jumping out of a plane with nothing, but a parachute attached to your back, we as humans have distilled fear to its essence that of adrenaline/epinephrine. While we seek fear in its purest form, the biological role of fear is to keep us aware, alert, and alive. The fear response evokes the fight or flight response and prepares the body to run screaming down the hallway or pick up a baseball bat and Babe Ruth the zombie’s head. Researchers have recently discovered and characterized new neuronal circuitry that modulates the fear response in an animal model. The ventral lateral geniculate nucleus (vLGN) is a prethalamic nucleus thought to primarily be a visual area that contains numerous GABAergic neurons and processes visual input from the layer-5 neurons of the visual cortex and the retina. It has been shown that a large portion of vLGN neurons exhibit receptive fields as well as respond to visual stimuli. Activity in the vLGN reflects the animal’s previous threat experience and is regulated by the perceived danger level of their environment. The vLGN controls both the escape response to approaching and imminent visual threats as well as the animal’s defensive behavior in an open and exposed environment. The vLGN acting as a neuronal security camera helps the animal avoid being eaten. It accomplishes this physical feat through the neuronal activity within this region. If neuronal activity is high in the vLGN, this prevents escape, whereas low neuronal activity in the vLGN initiates the escape response.Using a mouse model, the scientists were able to show this neuronal pattern by exposing the mouse to a visual threat stimulus within a new unexplored area, revealing that neuronal activity was decreased in the vLGN and further decreased when the mouse was reintroduced into the same area the visual threat was previously encountered. Moreover, in naïve mouse axonal activity in the vLGN was high when they no longer perceived the visual stimuli as a threat due to becoming acclimated to a perceived visible threat, realizing the visual stimuli had no adverse consequences. Furthermore, activity in the vLGN was highest when the mouse felt safest in their shelter. This neuronal circuity helps the animal to decide whether to act upon incoming perceived visual threats and to choose whether or not ignore or act upon the stimuli. The vLGN or the pregeniculate nucleus in primates/humans is one of the reasons we call the Ghostbuster’s when you see an invisible man sleeping in your bed or when you see a rotten shell of soulless corpse and you fight to stay alive your body starts to shiver for no mere mortal can resist the evil of the Thriller – Vincent Price.