Sample Solution

Event-related potentials (ERPs) are voltages generated by the brain due to sensory, motor, or cognitive stimuli. During ERPs, cortical pyramidal neurons fire action potentials as the brain is processing the stimuli. The summation of these postsynaptic potentials reflect the type of the ERP (Sur et al., 2009). For example, N1 waves is elicited when a auditory stimuli is presented (Sur et al., 2009). A P2 wave may be elicited in response to sensation seeking behavior (Sur et al., 2009). P3 waves may be elicited in response to unexpected target words (Sur et al., 2009). Studies have been conducted on patients in vegetative and minimally conscious states to investigate cortical functions by evaluating ERP responses to auditory cues. In a study done by Kotchoubey et al, all patients exhibited a ERP response, however the types of responses varied. Most patients displayed N1 and P2 waves while a third displayed P3 waves. Patients in the vegetative state were also found to have slightly lower ERP results compared to those of patients in the minimally conscious state (Kotchoubey et al., 2005). A study conducted by Perrin et al investigated semantic processing in patients in vegetative and minimally conscious states, by attempting to evoke ERPs using the auditory recordings of the patient’s name, revealed similar results. P3 waves were elicited in all minimally conscious patients and 60% of patients in a vegetative state (Perrin et al., 2006). Collectively, these studies imply that patients in vegetative and minimally conscious states have retained their auditory and language comprehension abilities. However, these results do not reflect consciousness, as ERPs can be generated in healthy unconscious patients as well.

Neurotransmitters

GABA (gamma-Aminobutyric acid) is an inhibitory neurotransmitter and glutamate is a excitatory neurotransmitter. Both modulate activity and communication between neurons (Pontes et al., 2013). After brain injuries, a surge of GABA and glutamate enter the brain. The presence of glutamate results in the ischemic microenvironment becoming stabilized as apoptotic brain cells absorb toxic metabolites (Clauss, 2010). However, the inhibition caused by GABA begins to dominate, causing a suppression of cell metabolism to protect the cells. Brain functions are gradually suppressed as well, which results in a loss of consciousness. Subsequently, GABA starts to flow from the brain to the blood and the brain becomes depleted of GABA (Clauss, 2010). GABA receptors may then become over sensitive to the presence of GABA