26.03 Cortical Spreading Depression

Cortical spreading depression can be viewed as a wave of transient neural inhibition (spontaneous and evoked activity) that progresses slowly over the cortex at 2-6 mm per minute. This wave of depression is preceded by a transient wave of intense excitation associated with very high extracellular K⁺ and reduced blood flow. Although the trigger of excitability is not known, accumulation of extracellular K⁺ due to enhanced excitation depolarises adjacent neurons, causing the phenomenon to spread. Changes in blood flow or spreading excitation and depression may initiate the headache. Moreover, the localised spreading depression may activate the trigeminal nucleus caudalis (of the central pain pathway), sensitising the central pain pathway.