A system for detecting a concussion-based cortical spreading depression, non-invasively in a subject, the system comprising: a portable, instrumented head-mountable detection unit comprising: a plurality of scalp surface DC-electroencephalogram (DC-EEG) electrodes configured in a high density electrode array spaced between about 0.5 cm and about 1.5 cm apart from one another to detect a set of real-time scalp DC electrical potential signals non-invasively from a brain area of the subject, and to transmit the real-time scalp DC electrical potential signals to an amplifier unit; and a ground electrode configured to detect a ground voltage when placed on a non-scalp area of the patient; said portable, instrumented head-mountable detection unit placed on a surface of a scalp area of a subject; an amplifier unit configured to amplify the detected electrical potential signals; and a computing device to detect the presence of the concussion-based cortical spreading depression, said computing device comprised of a detection algorithm system implemented by a processing unit comprising one or more processors and a non-transitory computer-readable memory containing programming instructions that, when executed, cause the processing unit to receive the amplified electrical potential signals and to implement the programming instructions to: receive the ground voltage from the ground electrode which is in contact with a non-scalp area of the patient; use the received ground voltage to determine the primary DC voltage, Vi, for each of the plurality of scalp electrodes; use the primary DC voltage, Vi, to calculate a derived virtual ground voltage (Vg) for the plurality of scalp electrodes; determine a derived electrode voltage (Vig) based on the mean of the derived virtual ground voltages (Vg) for each of the scalp electrodes; and determine whether the derived electrode voltages indicates a depression in a voltage level among a set of adjacent electrodes; and, if so, generate an output indicating that the subject is experiencing a concussion-based CSD, and a report indicating a level of the depression and the area to which the depression corresponds. a portable, instrumented head-mountable detection unit comprising: a plurality of scalp surface DC-electroencephalogram (DC-EEG) electrodes configured in a high density electrode array spaced between about 0.5 cm and about 1.5 cm apart from one another to detect a set of real-time scalp DC electrical potential signals non-invasively from a brain area of the subject, and to transmit the real-time scalp DC electrical potential signals to an amplifier unit; and a ground electrode configured to detect a ground voltage when placed on a non-scalp area of the patient; a plurality of scalp surface DC-electroencephalogram (DC-EEG) electrodes configured in a high density electrode array spaced between about 0.5 cm and about 1.5 cm apart from one another to detect a set of real-time scalp DC electrical potential signals non-invasively from a brain area of the subject, and to transmit the real-time scalp DC electrical potential signals to an amplifier unit; and a ground electrode configured to detect a ground voltage when placed on a non-scalp area of the patient; said portable, instrumented head-mountable detection unit placed on a surface of a scalp area of a subject; an amplifier unit configured to amplify the detected electrical potential signals; and a computing device to detect the presence of the concussion-based cortical spreading depression, said computing device comprised of a detection algorithm system implemented by a processing unit comprising one or more processors and a non-transitory computer-readable memory containing programming instructions that, when executed, cause the processing unit to receive the amplified electrical potential signals and to implement the programming instructions to: receive the ground voltage from the ground electrode which is in contact with a non-scalp area of the patient; use the received ground voltage to determine the primary DC voltage, Vi, for each of the plurality of scalp electrodes; use the primary DC voltage, Vi, to calculate a derived virtual ground voltage (Vg) for the plurality of scalp electrodes; determine a derived electrode voltage (Vig) based on the mean of the derived virtual ground voltages (Vg) for each of the scalp electrodes; and determine whether the derived electrode voltages indicates a depression in a voltage level among a set of adjacent electrodes; and, if so, generate an output indicating that the subject is experiencing a concussion-based CSD, and a report indicating a level of the depression and the area to which the depression corresponds. receive the ground voltage from the ground electrode which is in contact with a non-scalp area of the patient; use the received ground voltage to determine the primary DC voltage, Vi, for each of the plurality of scalp electrodes; use the primary DC voltage, Vi, to calculate a derived virtual ground voltage (Vg) for the plurality of scalp electrodes; determine a derived electrode voltage (Vig) based on the mean of the derived virtual ground voltages (Vg) for each of the scalp electrodes; and determine whether the derived electrode voltages indicates a depression in a voltage level among a set of adjacent electrodes; and, if so, generate an output indicating that the subject is experiencing a concussion-based CSD, and a report indicating a level of the depression and the area to which the depression corresponds.