What is Neurophysiology
Neurophysiology is the study of neuronal activity through neuronal electrogenesis, providing a functional assessment of the nervous system by examining electrical activity generated by nerve and muscle cells. 1
Core Definition and Scope
Neurophysiology examines how the nervous system functions at the cellular and electrical level, distinct from structural imaging approaches. 1 The field encompasses:
- Recording and analysis of electrical potentials generated during nerve and muscle cell activity 2
- Assessment of both central and peripheral nervous system function through neuronal electrogenesis 1
- Functional evaluation that parallels clinical examination but provides more quantitative, objective measurements 1
Primary Clinical Techniques
The two main neurophysiological techniques used in routine clinical practice are:
- Electroencephalogram (EEG): Reflects cortical neuronal activity modulated by diencephalic and brainstem influences, as well as metabolic and toxic factors 1
- Evoked Potentials (EPs): Measure discrete firing patterns of neurons in response to sensory stimuli or cognitive tasks, including visual EPs, somatosensory EPs, brainstem acoustic EPs, and cognitive EPs like the P300 paradigm 1, 2
Additional techniques include nerve conduction studies (measuring velocity of nerve impulses in myelinated nerves) and electromyography (assessing muscle innervation and neuromuscular junction function). 2
Clinical Applications and Utility
Neurophysiological testing serves several critical functions:
- Quantitative assessment of nervous system function that is more objective than clinical examination alone and less affected by age or education 1
- Detection of subclinical dysfunction in patients with normal consciousness, particularly useful in metabolic encephalopathies 1, 3
- Differential diagnosis to distinguish between various causes of altered mental status, including ruling out non-convulsive status epilepticus and drug-induced disturbances 1, 3
- Serial monitoring without learning effects, making these tests valuable for tracking disease progression or treatment response 1
- Assessment in difficult cases where clinical examination is limited, such as patients under muscle blockade or those with multiple comorbidities 1
Physiological Basis
The electrical activity measured in neurophysiology depends on:
- Neuronal activity sensitivity to energy-providing metabolic systems, electrolyte homeostasis, and clearance of toxic substances 1
- Complex cellular networks where neurons transmit information as pulsed electrical codes through axons, with modifiable synapses that enable learning and adaptation 4
- Integration of vascular, electrical, and cellular systems that maximize neuronal functioning and brain performance 5
Important Clinical Considerations
Neurophysiological tests are primarily investigational tools rather than routine diagnostic tests because they do not provide direct behavioral information about daily functioning. 1 While they can demonstrate important neurophysiological impairment, some patients may maintain normal functioning despite abnormal test results. 1
The main advantage over psychometric testing is the absence of learning effects on repeated testing, making neurophysiology particularly valuable for monitoring treatment efficacy over time. 1 However, effects on quality of life indices remain more clinically relevant for most treatment decisions. 1
Neurophysiology is complementary to neuroimaging—while imaging shows structure, neurophysiology reveals function, similar to how clinical examination assesses the nervous system. 1