Mennemeier lab mennemeiermarks@uams.edu

Dr Mennemeier has attempted to explain spatial neglect, a disabling neurological syndrome that follows damage to cortical systems in both the right and left cerebral hemispheres.  Patients with neglect are not aware of stimuli located opposite the side of brain injury.  Theories explain neglect as a disorder of spatial attention or mental representation but neglect is confounded by wide-spread cortical dysfunction.  So, patient with neglect have more than one type of problem.  In addition to attentional deficits, they are frequently under-aroused which can compromise many different cognitive functions. In our view, the challenge of explaining neglect lies in identifying components that are necessary and sufficient for neglect.

We recently identified a disorder of magnitude estimation in neglect that is orthogonal to deficits in spatial attention but just as important.  Magnitude estimation refers to judgments of stimulus intensity, how much of something is present, as opposed to spatial attention which concerns where something is located.  We learned that magnitude estimation is compromised in neglect and that it uniquely explains how much of a stimulus is neglected.  This discovery enabled us to resolve a paradox for neglect known as "the crossover effect".  Interested readers should either consult the reference provided or e-mail Dr Mennemeier (msmennemeier@uams.edu) for preprints or reprints.

Because patients with neglect are under-aroused and because arousal systems are fundamental to conscious perception, Dr Mennemeier has teamed up with Drs Garcia-Rill, Skinner, and Dornhoffer to learn how arousal is compromised in neglect and, more importantly, how it might be treated.  The graph shows P50 amplitude data obtained from one patient with behavioral signs of decreased arousal both before and immediately following a clinical procedure designed to temporarily increase arousal (CPT).  The P50 amplitude in response to an auditory click is sensitive to activity within the reticular activating system (RAS).  P50 amplitude is diminished before stimulation, normalized immediately following CPT, and at baseline after effects of CPT reside.  One goal of this research is to learn if under-aroused patients have the capacity to respond to arousing stimulation and if they can benefit from medications designed to increase arousal.

Mennemeier, M., Pierce, C.A., Chatterjee,A., Anderson, B, Jewell,G., Dowler,R., Woods,A.J.,  Glenn, T., and Mark,V.M.  Biases in attentional orientation and magnitude estimation explain crossover: neglect is a disorder of both.  Journal of Cognitive Neuroscience (in press).