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The fusiform gyrus (FG) is an important node in the face processing network, but knowledge of its causal role in face perception is currently limited. Recent work demonstrated that high frequency stimulation applied to the FG distorts the perception of faces in human subjects (Parvizi et al. []: J Neurosci 32:14915-14920). However, the timing of this process in the FG relative to stimulus onset and the spatial extent of FG's role in face perception are unknown. Here, we investigate the causal role of the FG in face perception by applying precise, event-related electrical stimulation (ES) to higher order visual areas including the FG in six human subjects undergoing intracranial monitoring for epilepsy. We compared the effects of single brief (100 μs) electrical pulses to the FG and non-face-selective visual areas on the speed and accuracy of detecting distorted faces. Brief ES applied to face-selective sites did not affect accuracy but significantly increased the reaction time (RT) of detecting face distortions. Importantly, RT was altered only when ES was applied 100ms after visual onset and in face-selective but not place-selective sites. Furthermore, ES applied to face-selective areas decreased the amplitude of visual evoked potentials and high gamma power over this time window. Together, these results suggest that ES of face-selective regions within a critical time window induces a delay in face perception. These findings support a temporally and spatially specific causal role of face-selective areas and signify an important link between electrophysiology and behavior in face perception. Hum Brain Mapp 38:2830-2842, 2017. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Reduced hippocampal N-acetyl aspartate (NAA) is commonly observed in patients with advanced, chronic temporal lobe epilepsy (TLE). It is unclear, however, whether an NAA deficit is also present during the clinically quiescent latent period that characterizes early TLE. This question has important implications for the use of MR spectroscopic imaging (MRSI) in the early identification of patients at risk for TLE. To determine whether NAA is diminished during the latent period, we obtained high-resolution (1)H spectroscopic imaging during the latent period of the rat pilocarpine model of human TLE. We used actively detuneable surface reception and volume transmission coils to enhance sensitivity and a semiautomated voxel shifting method to accurately position voxels within the hippocampi. During the latent period, 2 and 7 d following pilocarpine treatment, hippocampal NAA was significantly reduced by 27.5 +/- 6.9% (P < 0.001) and 17.3 +/- 6.9% (P < 0.001) at 2 and 7 d, respectively. Quantitative estimates of neuronal loss at 7 d (2.3 +/- 7.7% reduction; P = 0.58, not significant) demonstrate that the NAA deficit is not due to neuron loss and therefore likely represents metabolic impairment of hippocampal neurons during the latent phase. Therefore, spectroscopic imaging provides an early marker for metabolic dysfunction in this model of TLE.

Development and sex hormones play an important role in the expression of seizures. Sex-specific differences in the development of seizure suppressing neuronal networks may account, at least in part, for age- and sex related susceptibility to seizures. The substantia nigra pars reticulata is a site involved in the control of seizures. In adult male rats, there are two distinct GABAA sensitive regions within the substantia nigra pars reticulata, which mediate opposite effects in flurothyl seizures. Muscimol infused into the anterior region is anticonvulsant while similar infusions into the posterior region are proconvulsant. These two regions differ morphologically, and utilize different efferent networks. In contrast, in postnatal day 15 male rats, there is no such differentiation and muscimol infusions have only proconvulsant effects. The hallmark of the female substantia nigra pars reticulata is the fact that muscimol- mediated proconvulsant effects cannot be demonstrated in any region at any age. The sex-related difference in nigral seizure control may be related to the lack of testosterone in females. Accordingly, neonatal castration of males results in the loss of the proconvulsant region. The male type of the substantia nigra pars reticulata effects can be induced by exogenous testosterone administration in neonatally castrated male or in female rats. The phenotype of nigral GABAergic neurons, as characterized by GABAA receptor subunit composition, muscimol-induced electrophysiological responses, and connectivity of output networks may each be altered by the presence of testosterone. Better understanding of the influence of the endocrine system on brain development and neuronal activity may provide new insight into the treatment of age- and sex-dependent seizure disorders.

Neurologists caring for patients who have experienced a first seizure or who are at increased risk of seizures are concerned with two questions. First, at what point do seizures lesion the brain and create the conditions for unprovoked, recurrent seizures, i.e. epilepsy. And second, seizure-induced changes can be prevented pharmacologically following an initial prolonged seizure, or prophylactically in individuals deemed at high risk of epilepsy? The number, duration and severity of seizures each influence the likelihood that an individual will experience chronic seizure-induced brain damage. However, the thresholds for deleterious seizure-induced sequelae are not well understood. Will repeated brief seizures produce similar changes as a single prolonged seizure? Do permanent alterations of neuronal function result from a single brief seizure? How long can neurons resist damage caused by prolonged seizures? These are all questions of immediate clinical significance. The anatomical, synaptic and functional consequences of seizures have been most extensively studied in the hippocampus, an epileptogenic structure that plays a central role in the generation of temporal lobe seizures. In this review, we will discuss the spectrum of known hippocampal alterations in epilepsy and highlight mechanisms through which neuronal and synaptic changes accrue. In addition to discussing the effects of prolonged seizures on the hippocampus, we will also review current data regarding the effects of repeated brief seizures as well as the effect of a single brief seizure. We will also discuss the relevance of development and gender on the manifestations of seizure-induced damage, in order to begin to stratify the risk of seizure sequelae to different human populations depending on age, and - to a lesser extent - on gender. The decision whether to treat, and how to treat seizures, results from an understanding of the immediate and long-term risks to the patient of either recurrent seizures, or of seizure-induced brain damage. Paradigmatic to this type of decision is the assessment of febrile seizures, a common occurrence in childhood. Current clinical and laboratory data indicate that simple febrile seizures do not result in long-term brain injury. However, novel laboratory findings indicate that even "benign" febrile seizures may produce subtle long-term changes in neuronal behavior - such as altered synaptic function. The improved understanding of the mechanism producing these long term effects is a necessary first step in the development of neuroprotective treatments that can be applied either in the acute setting at the time of an initial prolonged seizure, or prophylactically in individuals most likely to high risk of developing epilepsy.