Sensorimotor organization in double cortex syndrome

Abstract

Subcortical band heterotopia is a diffuse malformation of cortical development related to pharmacologically intractable epilepsy. On magnetic resonance imaging (MRI), patients with "double cortex" syndrome (DCS) present with a band of heterotopic gray matter separated from the overlying cortex by a layer of white matter. The function and connectivity of the subcortical heterotopic band in humans is only partially understood. We studied six DCS patients with bilateral subcortical band heterotopias and six healthy controls using functional MRI (fMRI). In controls, simple motor task elicited contralateral activation of the primary motor cortex (M1) and ipsilateral activation of the cerebellum and left supplementary motor area (SMA). All DCS patients showed task-related contralateral activation of both M1 and the underlying heterotopic band. Ipsilateral motor activation was seen in 4/6 DCS patients. Furthermore, there were additional activations of nonprimary normotopic cortical areas. The sensory stimulus resulted in activation of the contralateral primary sensory cortex (SI) and the thalamus in all healthy subjects. The left sensory task also induced a contralateral activation of the insular cortex. Sensory activation of the contralateral SI was seen in all DCS patients and secondary somatosensory areas in 5/6. The heterotopic band beneath SI became activated in 3/6 DCS patients. Activations were also seen in subcortical structures for both paradigms. In DCS, motor and sensory tasks induce an activation of the subcortical heterotopic band. The recruitment of bilateral primary areas and higher-order association normotopic cortices indicates the need for a widespread network to perform simple tasks.

Functional organization of human visual cortex in occipital polymicrogyria

“…Given the profoundly abnormal cortical morphology in our patients, it is surprising to find intact visual function and organization within PMG, and this suggests either a considerable redundancy in cortical visual circuitry or a significant plasticity of the polymicrogyric cortex involved in the processing of visual inputs. These findings are in line with our previous observation in patients with subcortical band heteropia showing that the abnormally layered subcortical band may sustain normal sensorimotor function [Jirsch et al, 2006]. While visual organization remains intact in our PMG patients, it is less clear whether these grossly abnormal occipital areas are involved in the genesis of these patients' seizures as intracranial EEG studies were not performed.…”

Functional MRI in Malformations of Cortical Development: Activation of Dysplastic Tissue and Functional Reorganization

“…To date, the most extensive fMRI study, by Janszky et al, included 28 patients with MCD, among them 4 with subcortical heterotopia, 4 with subependymal or periventricular heterotopic nodules, 9 with polymicrogyria, and 8 with focal cortical dysplasia 13 . Additionally, Speer et al and Jirsch et al reported on a total of 9 patients with band heterotopia 15,19 …”

Disrupted Frontal Connections in Band Heterotopia Mapped by Diffusion Tensor Tractography

“…Previous research has demonstrated that there were two types of neuron populations in BHT: one that followed a normal pat- tern for migration and the other that did not reach the cortex but remained stranded in subcortical white matter because of failure of microtubule function due to the X-linked mutation [10,16]. (3) Regional specificity [18] may mainly account for these differences, as the different regions of interest (ROIs) were focused in these two studies. Due to the severe deficits of neurons in the outer cortex, the fibers stemming from them were stunted, sparse, and fragmentary (Figure 2a), and thus they could not traverse the heterotopic gray matter.…”