Visuo-motor pathways in humans revealed by event-related fMRI

Abstract

Whether different brain networks are involved in generating unimanual responses to a simple visual stimulus presented in the ipsilateral versus contralateral hemifield remains a controversial issue. Visuo-motor routing was investigated with event-related functional magnetic resonance imaging (fMRI) using the Poffenberger reaction time task. A 2 hemifield · 2 response hand design generated the ''crossed'' and ''uncrossed'' conditions, describing the spatial relation between these factors. Both conditions, with responses executed by the left or right hand, showed a similar spatial pattern of activated areas, including striate and extrastriate areas bilaterally, SMA, and M1 contralateral to the responding hand. These results demonstrated that visual information is processed bilaterally in striate and extrastriate visual areas, even in the ''uncrossed'' condition. Additional analyses based on sorting data according to subjects' reaction times revealed differential crossed versus uncrossed activity only for the slowest trials, with response strength in infero-temporal cortices significantly correlating with crossed-uncrossed differences (CUD) in reaction times. Collectively, the data favor a parallel, distributed model of brain activation. The presence of interhemispheric interactions and its consequent bilateral activity is not determined by the crossed anatomic projections of the primary visual and motor pathways. Distinct visuo-motor networks need not be engaged to mediate behavioral responses for the crossed visual field/ response hand condition. While anatomical connectivity heavily influences the spatial pattern of activated visuomotor pathways, behavioral and functional parameters appear to also affect the strength and dynamics of responses within these pathways.

Boundary Completion Is Automatic and Dissociable from Shape Discrimination

“…That is, both polarities of the electric field at the scalp are sampled by the electrodes included in this analysis, which is unsurprising, because the summed voltage across the scalp is zero at each instant in time (i.e., the definition of the average reference). There was also a main effect of hemiscalp (F (1,10) ϭ 9.22; p Ͻ 0.013), indicative of the generally larger responses over the right versus left hemiscalp [for similar VEP findings, see Murray et al (2002) and for comparable functional magnetic resonance imaging (fMRI) evidence, see Martuzzi et al (2006)]. No other main effects reached our 0.05 significance criterion.…”

Influence of age and gender in motor performance in healthy subjects

“…MEG studies during a simple RT task after temporally structured cues have shown activation of cerebellum, cingular cortex and sensorimotor cortex [57]. Finally, studies with event-related functional MRI during a VRT task have shown, both with responses executed by the left or right hand, a similar spatial pattern of activated areas, including striate and extrastriate visual areas in the occipital lobe bilaterally, and supplementary motor area and primary motor cortex contralateral to the responding hand, with variable thalamic activation [58]. SPECT scanning with 123 beta-CIT showed that simple RT is correlated with striatal DAT availability [50].…”

The behavioral relevance of multisensory neural response interactions

“…There is now evidence, at least in non-human primates, for both cortico-cortical (Cappe and Barone, 2005; Hackett et al, 2007a; Smiley et al, 2007) and cortico-thalamo-cortical (Hackett et al, 2007b; Cappe et al, 2009) pathways; whereby, auditory and somatosensory information can converge and interact. Whether there is any variation in the routing of responses that would in turn result in faster or slower reaction times is unknown in the case of auditory-somatosensory interactions, but there is evidence that suggests that such is occurring during a simple visual detection task (Saron et al, 2003; Martuzzi et al, 2006). While we cannot unequivocally rule out this latter possibility as a contributing mechanism, our analyses (both of the surface-recorded ERPs and source estimations thereof) would suggest that our effects derive from modulations in the strength of activity of a common network of brain regions (though the sensitivity of ERPs to activity in sub-cortical structures is limited).…”