Working memory (WM) has hardly been explored in non-psychotic relatives of schizophrenic patients despite its potential suitability as a neurocognitive endophenotype. Indeed, WM modalities, components and processes have rarely been compared in the same group of relatives. The present study examined neurocognitive performance in healthy siblings of schizophrenic patients, including both spatial and verbal WM modalities and tests tapping maintenance (Spatial Span Backwards and CPT-IP d') and manipulative (Letters and Numbers Sequencing) WM processes.
Methods: 68 schizophrenia patients, 38 healthy siblings and 63 controls were assessed on IQ, attention, memory, WM, and executive functions. Cluster A symptoms were screened out in siblings and controls.
Results: Siblings had an intermediate performance between that of schizophrenic patients and controls. They performed worse than controls on IQ, LNS, animal naming, backwards spatial span, phonemic fluency, numbers d', and forward spatial span.
Discussion: Consistent with the WM literature in schizophrenia, both verbal and spatial WM differed significantly between siblings and controls, suggesting that WM deficits are modality independent. Our results failed to support the hypothesis that tests tapping WM manipulative processes heavily loading on DLFPC are quantitatively more impaired in relatives and, therefore, more sensitive to liability for schizophrenia. However, firm conclusions cannot be drawn until more studies assessing both maintenance and manipulative WM processes in relatives are available.