ABSTRACT
BACKGROUND: Voluntarily opening or closing our eyes results in fundamentally different input patterns and expectancies. Yet it remains unclear how our brains and visual systems adapt to these ocular states. OBJECTIVE/HYPOTHESIS: We here used transcranial magnetic stimulation (TMS) to probe the excitability of the human visual system with eyes open or closed, in the complete absence of visual inputs. METHODS: Combining Bayesian staircase procedures with computer control of TMS pulse intensity allowed interleaved determination of phosphene thresholds (PT) in both conditions. We measured parieto-occipital EEG baseline activity in several stages to track oscillatory power in the alpha (8-12 Hz) frequency-band, which has previously been shown to be inversely related to phosphene perception. RESULTS: Since closing the eyes generally increases alpha power, one might have expected a decrease in excitability (higher PT). While we confirmed a rise in alpha power with eyes closed, visual excitability was actually increased (PT was lower) with eyes closed. CONCLUSIONS: This suggests that, aside from oscillatory alpha power, additional neuronal mechanisms influence the excitability of early visual cortex. One of these may involve a more internally oriented mode of brain operation, engaged by closing the eyes. In this state, visual cortex may be more susceptible to top-down inputs, to facilitate for example multisensory integration or imagery/working memory, although alternative explanations remain possible.
Subject(s)
Phosphenes , Sensory Thresholds , Visual Cortex/physiology , Adult , Alpha Rhythm , Eye Movements , Female , Humans , Male , Photic Stimulation , Transcranial Magnetic Stimulation , Visual PerceptionABSTRACT
We investigated the moderating influence of apathy, depression and transient mood changes on executive functions under best medical treatment and under postoperative stimulation-on and -off conditions in a sample of 33 patients with Parkinson's disease (PD) after deep brain stimulation of the subthalamic nucleus (STN), 33 PD patients with pharmacological treatment only and 34 healthy controls. In comparison to clinical and healthy control groups, DBS patients showed worse executive task performance and also more severe symptoms of depression and apathy. Apathy accounted for differences in stroop interference between groups. The effects of DBS on stroop interference were explained by increased state anxiety in the -off, so that DBS STN had no significant influence on test performance. Consideration of neuropsychiatric symptoms and acute mood changes is an important aspect when evaluating neuropsychological deficits in DBS patients.
