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Human fronto-tectal and fronto-striatal-tectal pathways activate differently during anti-saccades.

de Weijer AD, Mandl RC, Sommer IE, Vink M, Kahn RS, Neggers SF - Front Hum Neurosci (2010)

Bottom Line: In this study two possible pathways were investigated that might regulate automaticity of eye movements in the human brain; the cortico-tectal pathway, running directly between the frontal eye fields (FEF) and superior colliculus (SC) and the cortico-striatal pathway from the FEF to the SC involving the caudate nucleus (CN) in the BG.This increase in activity was lateralized with respect to anti-saccade direction in FEF zones connected to the SC but not for zones only connected to the CN.These findings suggest that activity along the contralateral FEF-SC projection is responsible for directly generating anti-saccades, whereas the pathway through the BG might merely have a gating function withholding or allowing a pro-saccade.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht Utrecht, Netherlands.

ABSTRACT
Almost all cortical areas in the vertebrate brain take part in recurrent connections through the subcortical basal ganglia (BG) nuclei, through parallel inhibitory and excitatory loops. It has been suggested that these circuits can modulate our reactions to external events such that appropriate reactions are chosen from many available options, thereby imposing volitional control over behavior. The saccade system is an excellent model system to study cortico-BG interactions. In this study two possible pathways were investigated that might regulate automaticity of eye movements in the human brain; the cortico-tectal pathway, running directly between the frontal eye fields (FEF) and superior colliculus (SC) and the cortico-striatal pathway from the FEF to the SC involving the caudate nucleus (CN) in the BG. In an event-related functional magnetic resonance imaging (fMRI) paradigm participants made pro- and anti-saccades. A diffusion tensor imaging (DTI) scan was made for reconstruction of white matter tracts between the FEF, CN and SC. DTI fiber tracts were used to divide both the left and right FEF into two sub-areas, projecting to either ipsilateral SC or CN. For each of these FEF zones an event-related fMRI timecourse was extracted. In general activity in the FEF was larger for anti-saccades. This increase in activity was lateralized with respect to anti-saccade direction in FEF zones connected to the SC but not for zones only connected to the CN. These findings suggest that activity along the contralateral FEF-SC projection is responsible for directly generating anti-saccades, whereas the pathway through the BG might merely have a gating function withholding or allowing a pro-saccade.

No MeSH data available.


Possible mechanisms for the FEF to regulate pro- and anti-saccade generation. The target is displayed as a black dot. For pro-saccades, the FEF contralateral to saccade direction can send a motor command directly to the SC in the same hemisphere and/or through the CN > SNpr (the so called ‘direct pathway’) (A). For anti-saccades, more scenarios are possible: the FEF ipsilateral to saccade direction could actively inhibition ipsilateral SC (through the ‘indirect pathway’) (B), thus inhibiting a pro-saccade. The FEF contralateral to saccade direction could excite the SC in the same hemisphere directly (C) or through the CN > GPe > SNpr (‘direct’) pathway (D), enforcing an anti-saccade over a pro-saccade. Also, a combination of scenario (B–D) could underly anti-saccade generation.
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Figure 1: Possible mechanisms for the FEF to regulate pro- and anti-saccade generation. The target is displayed as a black dot. For pro-saccades, the FEF contralateral to saccade direction can send a motor command directly to the SC in the same hemisphere and/or through the CN > SNpr (the so called ‘direct pathway’) (A). For anti-saccades, more scenarios are possible: the FEF ipsilateral to saccade direction could actively inhibition ipsilateral SC (through the ‘indirect pathway’) (B), thus inhibiting a pro-saccade. The FEF contralateral to saccade direction could excite the SC in the same hemisphere directly (C) or through the CN > GPe > SNpr (‘direct’) pathway (D), enforcing an anti-saccade over a pro-saccade. Also, a combination of scenario (B–D) could underly anti-saccade generation.

Mentions: Projections from the FEF/SEF to the SC are relayed through the BG in two parallel pathways using multiple inhibitory synapses (Hikosaka et al., 2000), see also Figure 1. The excitatory direct pathway starts with projections from the FEF to the caudate nucleus (CN) that inhibit the substantia nigra pars reticulata (SNpr) that itself normally tonically inhibits the SC. Therefore the direct pathway provides a net excitatory influence of the FEF over the SC as tonic inhibition of the SC is released when the pathway is activated. The inhibitory indirect pathway between FEF and SC through the BG runs from the FEF/SEF to the CN, the external segment of the globus pallidus (GPe), the sub-thalamic nucleus (STN), the SNpr, and finally the SC (Munoz and Everling, 2004). Although it was suggested that this pathway might prevent inappropriate automatic eye movements evoked by the SC (Munoz and Everling, 2004), many uncertainties remain how this complex system controls purposeful eye movements.


Human fronto-tectal and fronto-striatal-tectal pathways activate differently during anti-saccades.

de Weijer AD, Mandl RC, Sommer IE, Vink M, Kahn RS, Neggers SF - Front Hum Neurosci (2010)

Possible mechanisms for the FEF to regulate pro- and anti-saccade generation. The target is displayed as a black dot. For pro-saccades, the FEF contralateral to saccade direction can send a motor command directly to the SC in the same hemisphere and/or through the CN > SNpr (the so called ‘direct pathway’) (A). For anti-saccades, more scenarios are possible: the FEF ipsilateral to saccade direction could actively inhibition ipsilateral SC (through the ‘indirect pathway’) (B), thus inhibiting a pro-saccade. The FEF contralateral to saccade direction could excite the SC in the same hemisphere directly (C) or through the CN > GPe > SNpr (‘direct’) pathway (D), enforcing an anti-saccade over a pro-saccade. Also, a combination of scenario (B–D) could underly anti-saccade generation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2903195&req=5

Figure 1: Possible mechanisms for the FEF to regulate pro- and anti-saccade generation. The target is displayed as a black dot. For pro-saccades, the FEF contralateral to saccade direction can send a motor command directly to the SC in the same hemisphere and/or through the CN > SNpr (the so called ‘direct pathway’) (A). For anti-saccades, more scenarios are possible: the FEF ipsilateral to saccade direction could actively inhibition ipsilateral SC (through the ‘indirect pathway’) (B), thus inhibiting a pro-saccade. The FEF contralateral to saccade direction could excite the SC in the same hemisphere directly (C) or through the CN > GPe > SNpr (‘direct’) pathway (D), enforcing an anti-saccade over a pro-saccade. Also, a combination of scenario (B–D) could underly anti-saccade generation.
Mentions: Projections from the FEF/SEF to the SC are relayed through the BG in two parallel pathways using multiple inhibitory synapses (Hikosaka et al., 2000), see also Figure 1. The excitatory direct pathway starts with projections from the FEF to the caudate nucleus (CN) that inhibit the substantia nigra pars reticulata (SNpr) that itself normally tonically inhibits the SC. Therefore the direct pathway provides a net excitatory influence of the FEF over the SC as tonic inhibition of the SC is released when the pathway is activated. The inhibitory indirect pathway between FEF and SC through the BG runs from the FEF/SEF to the CN, the external segment of the globus pallidus (GPe), the sub-thalamic nucleus (STN), the SNpr, and finally the SC (Munoz and Everling, 2004). Although it was suggested that this pathway might prevent inappropriate automatic eye movements evoked by the SC (Munoz and Everling, 2004), many uncertainties remain how this complex system controls purposeful eye movements.

Bottom Line: In this study two possible pathways were investigated that might regulate automaticity of eye movements in the human brain; the cortico-tectal pathway, running directly between the frontal eye fields (FEF) and superior colliculus (SC) and the cortico-striatal pathway from the FEF to the SC involving the caudate nucleus (CN) in the BG.This increase in activity was lateralized with respect to anti-saccade direction in FEF zones connected to the SC but not for zones only connected to the CN.These findings suggest that activity along the contralateral FEF-SC projection is responsible for directly generating anti-saccades, whereas the pathway through the BG might merely have a gating function withholding or allowing a pro-saccade.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht Utrecht, Netherlands.

ABSTRACT
Almost all cortical areas in the vertebrate brain take part in recurrent connections through the subcortical basal ganglia (BG) nuclei, through parallel inhibitory and excitatory loops. It has been suggested that these circuits can modulate our reactions to external events such that appropriate reactions are chosen from many available options, thereby imposing volitional control over behavior. The saccade system is an excellent model system to study cortico-BG interactions. In this study two possible pathways were investigated that might regulate automaticity of eye movements in the human brain; the cortico-tectal pathway, running directly between the frontal eye fields (FEF) and superior colliculus (SC) and the cortico-striatal pathway from the FEF to the SC involving the caudate nucleus (CN) in the BG. In an event-related functional magnetic resonance imaging (fMRI) paradigm participants made pro- and anti-saccades. A diffusion tensor imaging (DTI) scan was made for reconstruction of white matter tracts between the FEF, CN and SC. DTI fiber tracts were used to divide both the left and right FEF into two sub-areas, projecting to either ipsilateral SC or CN. For each of these FEF zones an event-related fMRI timecourse was extracted. In general activity in the FEF was larger for anti-saccades. This increase in activity was lateralized with respect to anti-saccade direction in FEF zones connected to the SC but not for zones only connected to the CN. These findings suggest that activity along the contralateral FEF-SC projection is responsible for directly generating anti-saccades, whereas the pathway through the BG might merely have a gating function withholding or allowing a pro-saccade.

No MeSH data available.