Addiction – Overstimulation and ADHD

 

Observational studies conducted by Dr. Dimitri Christakis (Center for Child Health and Development) in humans have found associations between overstimulation in infancy via excessive television viewing and subsequent deficits in cognition and attention. As a member of the Christakis laboratory Julian S. Benedikt Ramirez developed and tested a mouse model of overstimulation whereby mice are subjected to audio (70 db) and visual stimulation (flashing lights) for six hours per day for a total of 42 days (Christakis et al. 2012). We use a variety of behavioral tests to examine the consequences of overstimulation, including the so called Light Dark Latency Test, Elevated Plus Maze, Novel Object Recognition, and Barnes Maze.  In all tests, overstimulated mice perform significantly worse compared to controls suggesting increased activity and risk taking, diminished short term memory, and decreased cognitive function (see figure below). These findings suggest that excessive non-normative stimulation during critical periods of brain development can have demonstrable untoward effects on subsequent neurocognitive function. In collaboration with the Ramirez laboratory we are now investigating how excessive stimulation alters brain circuitry. The Ramirez laboratory is interested in characterizing dopaminergic neurons and their firing properties (Mrejeru et al. 2011; see figure below), and preliminary data suggest that sensory overstimulation leads to increased hippocampal activity, decreased neurogenesis and increased gain to dopaminergic modulation. These effects are very different from those caused by the enriched environment paradigm (Ransohoff et al. 2008).