Cognitive outcome as part and parcel of clinical outcome in brain tumor surgery.

Although validated tools (neuropsychological tests, patient reported outcomes, mood and psychological profile) were first introduced many years ago in clinical practice, the impact of the tumor itself on patient cognition has not been extensively studied. Furthermore, while outcome research is evolving in an attempt to adapt the use of different tools to the preoperative and postoperative phases, the standard guidelines for evaluating outcome after brain surgery, by neurological examination and complication assessment, are frequently neglected in the current literature. This article attempts to provide an appraisal of the evidence for the impact of surgical treatment on cognitive function of brain tumor patients within the context of general outcome.

Blindsight following visual cortex deafferentation disappears with purple and red stimuli: a case study.

We employed a redundant signal effect (RSE) paradigm to ascertain the role of the superior colliculus (SC) in blindsight. The RSE consists of the speeding of reaction time (RT) to double versus single stimuli. One patient with a unilateral lesion of the optic radiation and consequent hemianopia showed a RSE with pairs of visual stimuli presented across the vertical meridian despite seeing only stimuli in the intact hemifield. However, when, instead of achromatic stimuli we used short or long wavelength stimuli the implicit RSE disappeared. This result raises the possibility that implicit chromatic processing in the affected hemifield might have a different neural substrate following deafferentation with respect to lesion of the primary visual cortex.

Evidence of midline retinal nasotemporal overlap in healthy humans: a model for foveal sparing in hemianopia?

The existence of midline retinal nasotemporal overlap in humans is controversial. Here we used the Poffenberger paradigm and monocular vision to assess the existence of a midline retinal area projecting to both hemispheres and of a possible differential contribution of the two hemiretinae. When brief visual stimuli were presented at 1 degrees eccentricity they were responded to equally quickly with either hand while at 6 degrees the hand on the same side as the stimulated hemifield was consistently faster than the contralateral hand. This pattern of results is consistent with a nasotemporal overlap at 1 degrees and a complete lateralization at 6 degrees . Both hemiretinae contribute to the overlap area which can be considered as responsible for foveal sparing in hemianopic patients.

Interhemispheric transfer and integration of imagined visual stimuli.

We employed two reaction time paradigms to find out whether imagined visual stimuli can be integrated between the two cerebral hemispheres. In a first experiment we found that interhemispheric transfer time, as assessed with the Poffenberger paradigm, was much longer for imagined than visible stimuli and this suggests that the callosal site of transfer is different in the two conditions. In a second experiment we found that interhemispheric summation, as assessed with the redundant signal effect paradigm, was present for both visible and imagined stimuli and could be accounted for by a neural coactivation mechanism rather than by a probabilistic explanation. Taken together, these results support the view that that there is an equivalence between perceptual and imagery processes that goes beyond early processing stages and includes the interhemispheric exchange of information.

Retinal eccentricity effects on reaction time to imagined stimuli.

To cast light on the possible neural substrate of visual imagery we tested normal participants and one hemianopic patient on simple reaction time (RT) to real and imagined visual stimuli. In one experiment participants were to detect as quickly as possible a luminous square presented at one out of two different retinal eccentricities. A well known effect with visual stimuli is that RT is slower for peripheral versus central stimuli. We found that imagined stimuli showed an eccentricity effect similar to that obtained with real stimuli. However, this was not the case in a patient with a hemianopic visual field loss (quadrantanopia) as a result of damage to the optic radiation. Even though the patient showed no difficulty in imaging stimuli in the affected hemifield she did not show an eccentricity effect as was the case in her intact side. In a second experiment, normal participants showed faster RT to stimuli of larger size with either real or imagined stimuli. Overall, these results show that visual perception and imagination share a similar visuotopic organisation that is disrupted following deafferentation of the visual cortex.

Attention and interhemispheric transfer: a behavioral and fMRI study.

When both detections and responses to visual stimuli are performed within one and the same hemisphere, manual reaction times (RTs) are faster than when the two operations are carried out in different hemispheres. A widely accepted explanation for this difference is that it reflects the time lost in callosal transmission. Interhemispheric transfer time can be estimated by subtracting RTs for uncrossed from RTs for crossed responses (crossed-uncrossed difference, or CUD). In the present study, we wanted to ascertain the role of spatial attention in affecting the CUD and to chart the brain areas whose activity is related to these attentional effects on interhemispheric transfer. To accomplish this, we varied the proportion of crossed and uncrossed trials in different blocks. With this paradigm subjects are likely to focus attention either on the hemifield contralateral to the responding hand (blocks with 80% crossed trials) or on the ipsilateral hemifield (blocks with 80% uncrossed trials). We found an inverse correlation between the proportion of crossed trials in a block and the CUD and this effect can be attributed to spatial attention. As to the imaging results, we found that in the crossed minus uncrossed subtraction, an operation that highlights the neural processes underlying interhemispheric transfer, there was an activation of the genu of the corpus callosum as well as of a series of cortical areas. In a further commonality analysis, we assessed those areas which were activated specifically during focusing of attention onto one hemifield either contra- or ipsilateral to the responding hand. We found an activation of a number of cortical and subcortical areas, notably, parietal area BA 7 and the superior colliculi. We believe that the main thrust of the present study is to have teased apart areas important in interhemispheric transmission from those involved in spatial attention.

Is blindsight in normals akin to blindsight following brain damage?

The aim of this chapter is to discuss evidence bearing on two related issues, namely, first, whether the neural pathways of subliminal perception are the same as those subserving suprathreshold perception. Second, whether the pathways for subliminal perception in normals are similar to those subserving blindsight in brain-damaged patients. As to the former question, the overall balance is in favor of the different-pathway hypothesis while a tentative answer to the second question might be that blindsight is basically similar to subliminal perception in normals. The differences undoubtedly existing between the two conditions depend mainly on the differences in the stimuli used to reveal them.