Spatial Neglect and Attention Networks

1. Spatial Neglect andAttention Networks YoungjinKang Baoyu Wang Zhiheng Zhang

2. 20. Figure 5a • Posner task: Attention reorienting • Both TPJ and VFC showed contralesional deficits • VFC also showed reorienting deficits in the ipsilesional field

3. 20. Figure 5b • Detection of behaviorally relevant stimuli • Detection deficits in neglect patients • Lager TRs to an ipsilesional auditory stimulus

4. 20. Figure 5c • Arousal deficits in neglect patients • TPJ patients showed a vigilance decrement

5. 21. It seems odd that arousal and neglect are connected. What is the nature of the connection? What hemispheric phenomena are involved? • Right hemisphere injury patients have lower arousal than left injury patients • An impairment of ability to sustain the arousal • Auditory counting test of arousal in neglect patients indicated a strong linkage between arousal and spatial deficits • Arousal related activations are associated in the ventral frontoparietal cortex

6. 22.So what to the authors believe about these issues concerning right hemisphere lateralization and the physiology of core non-spatial deficits? Tie together the other symptoms in neglect and the core deficits. • Reorienting of attention • Neuroimaging studies of healthy adults have shown that reorienting to stimuli in either visual field that are presented outside the focus of attention (stimulus-driven reorienting) recruits a right lateralized ventral attention network in TPJ and VFC, in conjunction with the dorsal network. • Detection of behaviorally relevant and novel stimuli • Right hemisphere dominance during target detection is observed in regions that are frequently associated with neglect (IPL, STG, IFG) and for visual targets in both left and right hemi-field. • Arousal and vigilance • Neuroimaging studies of arousal and vigilance have qualitatively reported right hemisphere dominance. Arousal-related activations are recorded more frequently in ventral cortex of the right than left hemisphere • Right Hemisphere lateralization of spatial deficits • Most widely accepted standard theory is that right hemisphere controls shift of attention to both sides of space while the left hemisphere only controls attention to the right side.

7. 23.Explain the blue box and Figure 6 Detection Reorienting Arousal

8. Right hemisphere dominance in vertebrates • The lateralization of these processes is supported by similar findings in other species. • “…The right hemisphere, the primary seat of emotional arousal, was at first specialized for detecting and responding to unexpected stimuli in the environment.” • Chicks: • Behavioral asymmetries arise partly from asymmetric light exposure prior to hatching • Mammals • Right hemisphere dominance for several nonspatial functions may partly reflect asymmetric brainstem projections.

9. “Dorsal vs. Ventral” & “Spatial vs. Nonspatial” -1 1. Nonspatial function, such as arousal, is right lateralized. 2. Increases in arousal bias attention to the left visual field, increasing left-field attention. 3. “Ventral area  Nonspatial function” vs. “Dorsal area  Spatial function” 4. Right ventral area stroke patients have non-spatial deficits (reduced vigilance and slowness even in his right visual field), and spatial neglects as well. “How are Ventral and Dorsal areas functionally connected ?”

10. “Dorsal vs. Ventral” & “Spatial vs. Nonspatial” -2 1. The link between “the damage to ventral regions” and “the abnormal physiology of dorsal regions”. 2. Hypoactivation of the right hemisphere caused by ventral damage reduce interactions between the ventral and dorsal attention networks. 3. The result is unbalanced interhemispheric physiological activity in the dorsal network 4. The right hemisphere dominance of neglect follows from the specific biases produced by right lateralized nonspatial mechanisms on the direction of spatial attention.