General Electronic Design

A number of single n-wire electrodes can be attached via amplifier-binary converter to a multiplex amplifier that would sequentially switch between large, "simultaneously recorded" electrical brain signals (Figure C.10B). This is possible since the switching properties of modern multiple amplifiers are many orders of magnitude faster than the electrical signals of the brain. Thus, the number of independent wires necessary to convey the information down to the terminals of the interface would be a small fraction of the total number of n-wires, and thus, inexpensive and robust microwires can be used along the catheter length.

Many technical issues concerning hardware problems, such as n-amplifiers and multiplex units, can in fact be solved by present technology. The actual size of the expected extracellular recording wiring is given in Figure C.11 by comparing the size of one-micrometer wire with the size of a capillary in the brain parenchyma. In this case, an individual Purkinje cell is drawn to show where the capillary spaces reside within the dendritic tree of such neurons. Note that the number of capillaries traversing each cell is numerous (in this particular case, more then 20). On the right inset is an electron micrograph of the same area that gives an accurate representation of the size relation between one such n-wire (in this case 0.9 micron) and the diameter of the smallest of capillaries in that portion of brain parenchyma.

Thus, at this point, the materials and methodology required to implement a mega electrode system are basically within our technology over the next decade.

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