Reorganization of Retinotopic Maps after Occipital Lobe Infarction

Abstract

We studied patient JS who had a right occipital infarct that encroached on visual areas V1, V2v and VP. When tested psychophysically, he was very impaired at detecting the direction of motion in random dot displays where a variable proportion of dots moving in one direction (signal) were embedded in masking motion noise (noise dots). The impairment on this Motion Coherence task was especially marked when the display was presented to the upper left (affected) visual quadrant, contralateral to his lesion. However, with extensive training, by 11 months his threshold fell to the level of healthy subjects. Training on the Motion Coherence task generalized to another motion task, the Motion Discontinuity task, on which he had to detect the presence of an edge that was defined by the difference in the direction of the coherently moving dots (signal) within the display. He was much better at this task at 8 than 3 months, and this improvement was associated with an increase in the activation of the human MT complex (hMT+) and in the kinetic occipital region (KO) as shown by repeated fMRI scans. We also used fMRI to perform retinotopic mapping at 3, 8 and 11 months after the infarct. We quantified the retinotopy and areal shifts by measuring the distances between the center of mass of functionally defined areas, computed in spherical surface-based coordinates. The functionally defined retinotopic areas V1, V2v, V2d and VP were initially smaller in the lesioned right hemisphere, but they increased in size between 3 and 11 months. This change was not found in the normal, left hemisphere, of the patient or in either hemispheres of the healthy control subjects. We were interested in whether practice on the motion coherence task promoted the changes in the retinotopic maps. We compared the results for patient JS with those from another patient (PF) who had a comparable lesion but had not been given such practice. We found similar changes in the maps in the lesioned hemisphere of PF. However, PF was only scanned at 3 and 7 months, and the biggest shifts in patient JS were found between 8 and 11 months. Thus, it is important to carry out a prospective study with a trained and untrained group so as to determine whether the patterns of reorganization that we have observed can be further promoted by training.

Relearning to See in Cortical Blindness

“…Both training tasks (global motion and static orientation discrimination) also decreased the size of the patients’ blind field, as defined by Humphrey automated perimetry (Huxlin and others 2009). Finally, Vaina and colleagues performed a different form of global motion discrimination training (Figure 2I) in a single hemianopic patient, and also reported significant improvement on the trained task, as well as on Humphrey automated perimetry and on discriminating motion-defined form (Vaina and others 2014). …”

“…It also begins to address the issue of whether recovered vision is completely normal. Improvement back to levels of performance measured in the intact hemifield of vision has been reported following specific training on direction range thresholds (Huxlin and others 2009), simple left-right motion discrimination (Huxlin and others 2009; Vaina and others 2014), high-contrast, coarse orientation discriminations (Huxlin and others 2009), and flicker detection of both luminance discs and letters (Raninen and others 2007). However, other visual faculties do not appear to recover completely.…”

“…Assessment of the comparative merits of different retraining paradigms is complicated by the fact that different groups have used different visual training and testing methods as well as different outcome measures. An exception is Humphrey automated perimetry with eye tracking, which has been used as an outcome measure by several groups (Chokron and others 2008; Das and others 2014; Huxlin and others 2009; Sahraie and others 2010; Sahraie and others 2013; Sahraie and others 2006; Trevathan and others 2012; Vaina and others 2014). However, beyond providing a measure of luminance detection sensitivity used to assess the size of visual field defects, it gives little information as to the quality of recovered vision.…”

On memories, neural ensembles and mental flexibility

“…In other words, that cues adjacent in the visual field induce responses that are also adjacent on the cortical surface (Vaina et al, 2014). Our focus was not on optimizing clustering but on preserving the spatial order of recording sites in the connectivity components.…”

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

“…Most prior neuroimaging studies on the properties of cortical reorganization and residual visual processing in CB involved case reports (Baseler et al, 1999;Bridge et al, 2010;Bridge et al, 2008;Dilks et al, 2007;Henriksson et al, 2007;Vaina et al, 2014). Only more recent investigations have examined larger patient cohorts (Ajina et al, 2015;Martin et al, 2012;Papanikolaou et al, 2014;Raemaekers et al, 2011).…”