Acute human brain responses to intracortical microelectrode arrays: challenges and future prospects

Abstract

The emerging field of neuroprosthetics is focused on the development of new therapeutic interventions that will be able to restore some lost neural function by selective electrical stimulation or by harnessing activity recorded from populations of neurons. As more and more patients benefit from these approaches, the interest in neural interfaces has grown significantly and a new generation of penetrating microelectrode arrays are providing unprecedented access to the neurons of the central nervous system (CNS). These microelectrodes have active tip dimensions that are similar in size to neurons and because they penetrate the nervous system, they provide selective access to these cells (within a few microns). However, the very long-term viability of chronically implanted microelectrodes and the capability of recording the same spiking activity over long time periods still remain to be established and confirmed in human studies. Here we review the main responses to acute implantation of microelectrode arrays, and emphasize that it will become essential to control the neural tissue damage induced by these intracortical microelectrodes in order to achieve the high clinical potentials accompanying this technology.

Keywords: biocompatibility; in vivo recording; intracortical microelectrode; neural prosthesis; neurosurgery.

Figure 1

Photographs showing the silicon-based Utah Electrode Array (UEA) and representative results of its implantation into human cortex. (A) Scanning electron micrograph of the UEA. (B) Single-unit responses recorded with the UEA from human temporal cortex (47 superimposed traces). (C) Astrocytes, labeled here with anti-glial fibrillary acidic protein antibody (GFAP) increase the thickness of their main processes, especially around electrode tracks (asterisk). (D) Resident microglial cells and blood-borne macrophages, labeled here with anti-CD45 antibody, become activated and migrate toward the electrodes. Note the electrode track filled with blood cells (asterisk) and a nearby blood vessel. Calibration bars = 50 μm.

Figure 2

Gross specimens of human temporal lobe implantations and scanning micrographs of the surface of the Utah Electrode Array after acute implantation in human brain. (A) Placement of an electrode array in temporal cortex. (B) Once the array has been removed there are some evident microhemorrhages. (C) Horizontal section showing blood in the outermost electrode tracks and petechial hemorrhages (white arrows) located below the tip of the electrodes. (D) Detail of the petechial hemorrhages. (E) Scanning electron micrograph of an electrode tip. Many red blood cells appear in close contact with electrode materials. (F) Detail of the red blood cells on the surface of the microelectrodes. Calibration bars A, B, C and D= 2 mm.