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Review
, 192 (2), 149-65

Techniques and Devices to Restore Cognition

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Review

Techniques and Devices to Restore Cognition

Mijail Demian Serruya et al. Behav Brain Res.

Abstract

Executive planning, the ability to direct and sustain attention, language and several types of memory may be compromised by conditions such as stroke, traumatic brain injury, cancer, autism, cerebral palsy and Alzheimer's disease. No medical devices are currently available to help restore these cognitive functions. Recent findings about the neurophysiology of these conditions in humans coupled with progress in engineering devices to treat refractory neurological conditions imply that the time has arrived to consider the design and evaluation of a new class of devices. Like their neuromotor counterparts, neurocognitive prostheses might sense or modulate neural function in a non-invasive manner or by means of implanted electrodes. In order to paint a vision for future device development, it is essential to first review what can be achieved using behavioral and external modulatory techniques. While non-invasive approaches might strengthen a patient's remaining intact cognitive abilities, neurocognitive prosthetics comprised of direct brain-computer interfaces could in theory physically reconstitute and augment the substrate of cognition itself.

Figures

Fig. 1
Fig. 1
Restoration or augmentation of a connection between two brain areas by means of paired electrode arrays. (a) Two brain areas are reciprocally linked by uncinate fibers in the white matter. (b) A subcortical stroke destroys the white matter tract that linked the areas. (c) Multi-electrode arrays implanted in each area are connected to a medical device or computer system that functionally restores the interconnection by means of recording and stimulation. (d) Two cortical areas are already physically linked by uncinate fibers. (e) Correlated spike-triggered stimulation or firing induces plasticity in connecting synapses. (f) The two areas are now more strongly coupled.
Fig. 2
Fig. 2
Connection rules. (a) Spike-triggered stimulation. (b) Spike-triggered stimulation gained by a weighting rule. (c) Artificial Hebbian or BCM learning rule, comparing the relative spike timing of two units to decide if and at what frequency to stimulate one of the units. (d) Multiple neurons coupled to each other via artificial synapses in a neural network. (e) Connections routed through a neural circuit model or ectopic neural tissue.
Fig. 3
Fig. 3
A hypothetical computer thalamocortical ‘organ’ to represent and process web browser, relational database or other computer-based data. The artificial relay and primary cortices send their outputs to the real pulvinar nucleus and association cortex of the patient.
Fig. 4
Fig. 4
Autologous ectopic neural tissue to restore cognitive function lost to brain injury, congenital anomalies, or degenerative conditions. (1) The olfactory epithelium is biopsied. (2) Neural progenitor cells are isolated and cell lines are created by addition of growth factors. In addition, cells may be genetically modify to express novel proteins, such as photo-sensitive channelrhodopsin. (3) Cell types are cultured upon a bidirectional silicon chip. Neurons may be placed directly on the gate oxide of transistors or on conductive disk electrodes. The cell assembly may be structured in three dimensions and seeded with vascular progenitors to ensure vascularization. (4) The ectopic neural tissue assembly is implanted chronically into the patient. The ectopic tissue is bidirectionally linked to one or more sensor-stimulator devices implanted in the brain by means of ultra-high-bandwidth fiber optic conduits.
Fig. 5
Fig. 5
The electrical activity captured by electrodes implanted above and within the brain are mapped on to artificial cortex. The layers V and VI outputs of the metacortex stream back to both association area (as shown) as well as to primary A1, V1, S1.

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