Interhemispheric neural summation in the split brain: effects of stimulus colour and task

Abstract

Four split-brained subjects, two subjects with agenesis of the corpus callosum, and 14 normal subjects performed two tasks requiring responses to red or green disks, briefly presented either singly in the left visual field, singly in the right visual field, or simultaneously in both visual fields. In Experiment 1, simple reaction times to these stimuli, regardless of colour, were recorded (the Go-Both Task), and found to be faster to bilateral-redundant stimulus pairs, than to single stimuli. This so-called "redundancy gain" was much larger for acallosal or split-brained subjects than for normal subjects and exceeded the predictions of a race model, implying neural summation. Experiment 2 used the same stimuli, but subjects were required to respond only to stimuli of a designated colour (the Go/No-Go Task). Redundant target stimuli produced neural summation, while stimuli pairs that included a non-target stimulus did not. These results suggest that neural summation in the acallosal or split brain involves the convergence of response-associated activation, and that redundant sensory processes are not sufficient.

Age-related differences in interhemispheric visuomotor integration measured by the redundant target effect.

“…There are, however, studies (Miniussi, Girelli, & Marzi, 1998;Savazzi & Marzi, 2002;Roser & Corballis, 2003) that report enhanced bilateral RTEs in normal participants, supporting the coactivation model and suggesting that RTEs are not due entirely to statistical facilitation.…”

“…The present study investigates age effects on the bilateral RTE and is motivated by the considerable, and growing, literatures that describes age effects on functional asymmetry (Cabeza, 2002;Park & Reuter-Lorenz, 2009) and interhemispheric structural connectivity Raz & Rodrigue, 2006), as well as previous demonstrations of enhanced RTEs in cases in whom interhemispheric callosal transfer is impaired (Roser & Corballis, 2002;Roser & Corballis, 2003;Roser, et al, in press;Schulte et al, 2006). The study, therefore, addresses a type of redundancy gain for which there are good reasons for expecting age effects to manifest.…”

Fiber tract-driven topographical mapping (FTTM) reveals microstructural relevance for interhemispheric visuomotor function in the aging brain

“…The RTE paradigm (Corballis, 2002) is used to study how the left and right cerebral hemisphere communicate to enhance performance beyond the processing capacities of a single hemisphere (Marks and Hellige, 2003) by comparing paired with single targets presented to one or both visual hemifields (for a review, see Schulte and Müller-Oehring, 2010). Typically, responses are faster to stimulus pairs than single stimuli (Iacoboni and Zaidel, 2003; Miller, 1986; Mordkoff and Yantis, 1991; Roser and Corballis, 2003; Savazzi and Marzi, 2004; Schulte et al, 2004, 2005) with performance advantages from bilateral redundant targets indicating hemispheric resource sharing to make this redundant targets process more efficient (Maertens and Pollmann, 2005). …”

Brain Commissural Anomalies

“…In split-brain patients, however, several investigators have noted that transfer of some types of visual information is usually spared (Eviatar & Zaidel, 1994;Uddin et al, 2008).The condition that cortical commissures are no longer available some information can be transferred between the hemispheres through subcortical pathways (Funnell et al, 2000) by the subcortical coordination of cortical networks (Uddin et al, 2008). In regard to involvement of the corpus callosum in lower-level visuomotor functions, split-brain research indicates that the corpus callosum acts in an inhibitory fashion within a subcortico-cortical network Roser & Corballis, 2003), while recent research on callosal degradation without disconnection have shown cooperative role for the corpus callosum (Schulte & Müller-Oehring, 2010) in conscious perception (Marzi et al, 1996;Müller-Oehring et al, 2009). In addition to mentioned functions, recently the enhanced redundancy gain (co-activation model) (Bucur et al, 2005;Schulte et al, 2006;Turatto et al, 2004) and mediate interhemispheric processing advantages Iacoboni et al, 2000;Roser & Corballis, 2003) a possible role for the corpus callosum are reported.…”

“…In regard to involvement of the corpus callosum in lower-level visuomotor functions, split-brain research indicates that the corpus callosum acts in an inhibitory fashion within a subcortico-cortical network Roser & Corballis, 2003), while recent research on callosal degradation without disconnection have shown cooperative role for the corpus callosum (Schulte & Müller-Oehring, 2010) in conscious perception (Marzi et al, 1996;Müller-Oehring et al, 2009). In addition to mentioned functions, recently the enhanced redundancy gain (co-activation model) (Bucur et al, 2005;Schulte et al, 2006;Turatto et al, 2004) and mediate interhemispheric processing advantages Iacoboni et al, 2000;Roser & Corballis, 2003) a possible role for the corpus callosum are reported. In regard to this question, how the corpus callosum mediates this transfer?…”