Brain-damaged patients with lesion or dysfunction involving the parietal cortex may show a variety of neuropsychological impairments involving spatial cognition. The more frequent and disabling deficit is the syndrome of unilateral spatial neglect that, in a nutshell, consists in a bias of spatial representation and attention ipsilateral to of extrapersonal, personal (ie, the body) space, or both, toward the side of the hemispheric lesion. The deficit is more frequent and severe after damage to the right hemisphere, involving particularly the posterior-inferior parietal cortex at the temporo-parietal junction. Damage to these posterior parietal regions may also impair visuospatial short-term memory, which may be associated with and worsen spatial neglect. The neural network supporting spatial representation, attention and short-term memory is, however, more extensive, including the right premotor cortex. Also disorders of drawing and building objects (traditionally termed constructional apraxia) are a frequent indicator of posterior parietal damage in the left and in the right hemispheres. Other less frequent deficits, which, however, have a relevant localizing value, include optic ataxia (namely, the defective reaching of visual objects, in the absence of elementary visuo-motor impairments), which is typically brought about by damage to the superior parietal lobule. Optic ataxia, together with deficits of visual attention, of estimating distances and depth, and with apraxia of gaze, constitutes the severely disabling Balint-Holmes' syndrome, which is typically associated with bilateral posterior parietal and occipital damage. Finally, lesions of the posterior parietal lobule (angular gyrus) in the left hemisphere may bring about a tetrad of symptoms (left-right disorientation, acalculia, finger agnosia, and agraphia) termed Gerstmann's syndrome, that also exists in a developmental form.

Studies showing facilitation of behavioural performance by transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS) in sensory and perceptual domains, spatial attention, working memory, and executive and emotional tasks are reviewed. In these domains the performance of neurologically unimpaired participants may be modulated, with behavioural facilitation or interference, by TMS, and by tDCS. The mapping of the frequency-dependent effects of TMS, and of the polarity-dependent effects of tDCS on behaviour does not systematically and mechanistically result in an increase or decrease of behavioural performance. Factors such as the parameters of the cerebral stimulation (localisation, duration, intensity), and the features of the task (complexity, phase of training) contribute to determine the final net effect on the participants' performance. Non-invasive brain stimulation (NIBS), which modulates learning, and appears to have, under some conditions, long lasting effects, is a promising tool to be used in the rehabilitation of a variety of neurological and cognitive disorders, that typically involve repeated behavioural training sessions.