ABSTRACT
OBJECTIVE: To identify features of BOLD signal change associated with interictal epileptiform discharges (IEDs) in a heterogeneous group of focal epilepsy patients. METHODS: EEG/fMRI studies in 27 focal epilepsy patients were reviewed with attention given to the extent and location of the IED and the resulting pattern of BOLD signal change. Second order group analysis was used to identify common features. RESULTS: fMRI results provided novel clinical information for individual patients. We identified a significant common node within the ipsilateral piriform cortex as well as patterns involving distant cortical or subcortical areas. CONCLUSION: Despite the heterogeneity of IEDs in focal epilepsy, there are important common features underpining IEDs with a highly significant fMRI node in the ipsilateral piriform cortex. SIGNIFICANCE: There are important common features in the networks involved in IEDs in patients with a heterogeneous range of epileptogenic foci. We confirm that the piriform cortex is a common node underlying IEDs in patients with focal epilepsy and so provides a target for further study and potential therapy. We describe important features of BOLD signal change that accompany focal and diffuse IEDs that will help researchers and clinicians navigate the sometimes complex findings revealed by these studies.
Subject(s)
Epilepsies, Partial/physiopathology , Adolescent , Adult , Brain/physiopathology , Child , Electroencephalography/methods , Female , Humans , Magnetic Resonance Imaging/methods , Male , Middle Aged , Nerve Net/physiology , Young AdultABSTRACT
It has been proposed that the underlying epileptic process is mediated by changes in both excitatory and inhibitory circuits leading to the formation of hyper-excitable seizure networks. In this review we aim to shed light on the many physiological factors that modulate excitability within these networks. These factors have been discussed extensively in many reviews each as a separate entity and cannot be extensively covered in a single manuscript. Thus for the purpose of this work in which we aim to bring those factors together to explain how they interact with epilepsy, we only provide brief descriptions. We present reported evidence supporting the existence of the epileptic brain in several states; interictal, peri-ictal and ictal, each with distinct excitability features. We then provide an overview of how many physiological factors influence the excitatory/inhibitory balance within the interictal state, where the networks are presumed to be functioning normally. We conclude that these changes result in constantly changing states of cortical excitability in patients with epilepsy.
Subject(s)
Cerebral Cortex/physiopathology , Epilepsy/physiopathology , Aging/physiology , Blood Glucose/metabolism , Cerebral Cortex/growth & development , Chronic Disease , Electroencephalography , Female , Hormones/metabolism , Humans , Male , Pregnancy , Sleep/physiology , Stress, Psychological/metabolism , WakefulnessABSTRACT
OBJECTIVE: We used transcranial magnetic stimulation to investigate the effect of diurnal variability on cortical excitability in patients with epilepsy. METHODS: Thirty drug-naive patients with epilepsy (20 idiopathic generalized epilepsy [IGE], including 10 juvenile myoclonic epilepsy [JME], and 10 focal epilepsy) and 10 control subjects without epilepsy were studied both early in the morning and late in the afternoon. We measured the mean motor thresholds and constructed recovery curves at short (2-15 msec) and long (50-400 msec) interstimulus intervals. RESULTS: An increase in cortical excitability indicated by decreased short and long intracortical inhibition was observed early in the morning compared to the afternoon in patients with JME. In other IGE syndromes, there was decreased long intracortical inhibition only. No effect was found in subjects with focal epilepsy or controls without epilepsy. CONCLUSION: Cortical excitability measured by transcranial magnetic stimulation increases early in the morning in patients with idiopathic generalized epilepsy, particularly in juvenile myoclonic epilepsy, but not in subjects with focal epilepsy or controls without epilepsy. This may explain the increased seizure susceptibility in this cohort at this time of day.
Subject(s)
Circadian Rhythm/physiology , Epilepsy, Generalized/physiopathology , Epilepsy/physiopathology , Adolescent , Adult , Cerebral Cortex/physiopathology , Cohort Studies , Dominance, Cerebral/physiology , Evoked Potentials/physiology , Evoked Potentials, Motor/physiology , Female , Functional Laterality/physiology , Humans , Male , Middle Aged , Myoclonic Epilepsy, Juvenile/physiopathology , Neural Inhibition/physiology , Predictive Value of Tests , Reaction Time/physiology , Sleep/physiology , Transcranial Magnetic Stimulation , Wakefulness/physiology , Young AdultABSTRACT
OBJECTIVE: To use transcranial magnetic stimulation (TMS) to investigate the hypothesis that sleep deprivation increases cortical excitability in people with epilepsy. METHODS: We performed paired pulse TMS stimulation, using a number of interstimulus intervals (ISIs) on each hemisphere of 30 patients with untreated newly diagnosed epilepsy (15 idiopathic generalized epilepsy [IGE] and 15 focal epilepsy) and on the dominant hemisphere of 13 healthy control subjects, before and after sleep deprivation. RESULTS: Both hemispheres in patients with IGE and the hemisphere ipsilateral to the EEG seizure focus in those with focal epilepsy showed an increase in cortical excitability following sleep deprivation at a number of ISIs. This change in excitability was most prominent in the patients with IGE. Although there were minor changes after sleep deprivation in control subjects and the contralateral hemisphere in the focal epilepsy group seen at the 250-millisecond ISI, it was less than in the other groups. CONCLUSIONS: Sleep deprivation increases cortical excitability in epilepsy; the pattern of change is syndrome dependent.
