Towards a functional topography of sensory gating areas: Invasive P50 recording and electrical stimulation mapping in epilepsy surgery candidates

Abstract

The filtering of sensory information, also referred to as "sensory gating", is impaired in various neuropsychiatric diseases. In the auditory domain, sensory gating is investigated mainly as a response decrease of the auditory evoked potential component P50 from one click to the second in a double click paradigm. In order to relate deficient sensory gating to anatomy, it is essential to identify the cortical structures involved in the generation of P50. However, the exact cerebral topography of P50 gating has remained largely unknown as yet. In a group of 17 patients with drug-resistant focal epilepsy, P50 was recorded invasively via subdural electrodes, and the topography of functionally indispensable ("eloquent") cortices was obtained by electrical stimulation mapping. These eloquent areas were involved in language, motor, and sensory functions. P50 could be identified in 13 patients in either temporal (n = 8) or midfrontal sites (n = 5). There were 6 occurrences (in 5 patients) of overlap of sites with maximal P50 responses and eloquent areas. Those were auditory (n = 1), supplementary sensorimotor (n = 3), primary motor (n = 1), and supplementary negative motor (n = 1). Results suggest that the early stage of sensory gating already involves a top-down modulation of sensory input by frontal areas.

P50 sensory gating is related to performance on select tasks of cognitive inhibition

“…As in the cognitive inhibition tasks, there is increasingly more evidence to suggest frontal cortex involvement in P50 sensory gating (Grunwald et al, 2003; Korzyukov et al, 2007; Kurthen et al, 2007; Weisser et al, 2001). Both fMRI (Marlow-O’Conner, 2005; Tregellas et al, 2007) and lesion (Knight, Staines, Swick, & Chao, 1999) paradigms have provided evidence for bilateral recruitment of DLPFC in gating.…”

Pattern of P50 suppression deficit in patients with epilepsy and individuals with schizophrenia

“…Kurthen et al analyzing epilepsy surgery candidates on standard therapy with anticonvulsant drug polytherapy, said that the drugs might systematically alter the P50 responses. On the other hand, they did not find any difference in responses comparing patients under complete drug withdrawal and patients under anticonvulsive treatment 22 . It seems unlikely that these medications may affect P50 suppression since no significant differences between the groups of patients with epilepsy were found, although just one of our patients was not taking anticonvulsive drugs.…”

“…However, suppression deficit was smaller than that found in individuals with schizophrenia. Few studies have analyzed the P50 auditory evoked potential in patients with epilepsy 14,[21][22][23][24] . One of them has evaluated the double-click paradigm, but it did not study the existence of a suppression deficit 14 .…”

“…Few studies about P50 suppression in patients with epilepsy have been found in the literature 14,[21][22][23][24] . Epilepsy may affect several brain structures that are important for the functioning of the sensory filter.…”

Schizophrenia diagnosis and anterior hippocampal volume make separate contributions to sensory gating

“…Based on this finding, further research is warranted to investigate other candidate brain regions that are known to be functionally impaired in schizophrenia. For example, intrahemispheric gating ratio has been linked to reduced schizophrenia STG cortical thickness (Thoma et al, 2004), and recent depth-electrode research in patients with epilepsy has suggested that medial frontal and sensory-motor cortex are also critical for gating (Kurthen et al, 2007). …”