A Computational Modeling Reveals That Strength of Inhibitory Input, E/I Balance, and Distance of Excitatory Input Modulate Thalamocortical Bursting Properties

The thalamus is a brain structure known to modulate sensory information before relaying to the cortex. The unique ability of a thalamocortical (TC) neuron to switch between the high frequency burst firing and single spike tonic firing has been implicated to have a key role in sensory modulation including pain. Of the two firing modes, burst firing, especially maintaining certain burst firing properties, was suggested to be critical in controlling nociceptive behaviors. Therefore, understanding the factors that influence burst firing properties would offer important insight into understanding sensory modulation. Using computational modeling, we investigated how the balance of excitatory and inhibitory inputs into a TC neuron influence TC bursting properties. We found that intensity of inhibitory inputs and the timing of excitatory input delivery control the dynamics of bursting properties. Then, to reflect a more realistic model, excitatory inputs delivered at different dendritic locations—proximal, intermediate, or distal—of a TC neuron were also investigated. Interestingly, excitatory input delivered into a distal dendrite, despite the furthest distance, had the strongest influence in shaping burst firing properties, suggesting that not all inputs equally contribute to modulating TC bursting properties. Overall, the results provide computational insights in understanding the detailed mechanism of the factors influencing temporal pattern of thalamic bursts.

Effects of 5HT1A Activation on Gating Profile Following 5HT Depletion in Rats Lacking Social Attachment Since Weanling

OBJECTIVE: Central 5-HT1A receptor is involved in the modulation of sensorimotor gating function. However, its precise role is not clearly defined in developmentally social deprived (isolation rearing, IR) rats featured with impaired sensorimotor gating ability. We therefore aimed to examine the effects of 5HT1A activation on acoustic startle response (ASR) and prepulse inhibition (PPI) in IR rats in a condition of compromised presynaptic 5-HT functions. METHODS: Social control (SOC) and IR rats received an intracerebraoventricular (ICV) injection of 5-HT depletor, 5,7-DHT. Seven days later rats entered a protocol of 8-OH-DPAT, a 5-HT1A agonist, in which locomotor activity, ASR and PPI and their tissue levels of 5-HT were measured. RESULTS: Our results found that both IR and 5,7-DHT decreased the tissue concentration of 5-HT. IR-induced hyperactivity and gating impairment were unaffected by 5-HT depletion. 8-OH-DPAT strengthened the ASR in IR but not SOC rats and the drug-reduced PPI could be adjusted by 5,7-DHT pretreatment. 8-OH-DPAT at 100 μg/kg enhanced PPI in 5-HT-depleted SOC rats. However for IR rats, 8-OH-DPAT strengthened PPI in sham rats but downgraded it in depletion condition. CONCLUSION: The integrity of central 5-HT system is important to 5-HT1A-modulated sensorimotor gating in isolation-reared rats.

Effects of Ketamine on Basal Gamma Band Oscillation and Sensory Gating in Prefrontal Cortex of Awake Rats / 神经科学通报·英文版

Gamma band oscillation (GBO) and sensory gating (SG) are associated with many cognitive functions. Ketamine induces deficits of GBO and SG in the prefrontal cortex (PFC). However, the time-courses of the effects of different doses of ketamine on GBO power and SG are poorly understood. Studies have indicated that GBO power and SG have a common substrate for their generation and abnormalities. In this study, we found that (1) ketamine administration increased GBO power in the PFC in rats differently in the low- and high-dose groups; (2) auditory SG was significantly lower than baseline in the 30 mg/kg and 60 mg/kg groups, but not in the 15 mg/kg and 120 mg/kg groups; and (3) changes in SG and basal GBO power were significantly correlated in awake rats. These results indicate a relationship between mechanisms underlying auditory SG and GBO power.

The Meaning of P50 Suppression: Interaction of Gamma and Alpha Waves

OBJECTIVES: Sensory gating dysfunctions in patients with schizophrenia and bipolar disorder have been investigated through two similar methods ; P50 suppression and prepulse inhibition paradigms. However, recent studies have demonstrated that the two measures are not correlated but rather constitute as distinct neural processes. Recent studies adopting spectral frequency analysis suggest that P50 suppression reflects the interaction between gamma and other frequency bands. The aim of the present study is to investigate which frequency component shows more significant interaction with gamma band. METHODS: A total of 108 mood disorder patients and 36 normal subjects were included in the study. The P50 responses to conditioning and test stimuli with an intra-pair interval of 500 msec were measured in the study population. According to P50 ratio (amplitude to the test stimulus/amplitude to the conditioning stimulus), the subjects with P50 ratio less than 0.2 were defined as suppressed group (SG) ; non-suppressed group (NSG) consisted of P50 ratio more than 0.8. Thirty-five and 25 subjects were included in SG and NSG, respectively. Point-to-point correlation coefficients (PPCCs) of both groups were calculated between two time-windows : the first window (S1) was defined as the time-window of one hundred millisecond after the conditioning auditory stimulus and the second window (S2) was defined as the time-window of 100 msec after the test auditory stimulus. Spectral frequency analysis was performed to investigate which frequency band results in the difference of PPCC between SG and NSG. RESULTS: Significant reduction of PPCC between S1 and S2 was observed in the SG (Pearson's r = 0.24), compared to PPCC of the NSG (r = 0.58, p < 0.05). In spectral frequency analysis, gamma band showed "phase-reset" and similar responses after the two auditory stimuli in suppressed and non-suppressed group. However in the case of alpha band, comparison showed significantly low PPCC in SG (r = -0.14) compared to NSG (r = 0.36, p < 0.05). This may be reflecting "phase-out" of alpha band against gamma band at approximately 50 msecs after the test stimulus in the SG. CONCLUSIONS: Our study suggests that normal P50 suppression is caused by phase-out of alpha band against gamma band after the second auditory stimulus. Thus it is demonstrated that normal sensory gating process is constituted with attenuated alpha power, superimposed on consistent gamma response. Implications of preserved gamma and decreased alpha band in sensory gating function are discussed.

Impaired prepulse inhibition of acoustic startle in Chinese patients with first-episode, medication-naïve schizophrenia / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Patients with schizophrenia have prominent abnormality in information processing that can be observed by measures of prepulse inhibition (PPI) of acoustic startle reflex and PPI deficits have been considered as a candidate endophenotypic marker of schizophrenia. However, there has been little information on PPI and related measures in Chinese patients with schizophrenia. The research was to explore the deficits of acoustic startle reflex that might exist in Chinese patients with schizophrenia.</p><p><b>METHODS</b>Startle response to acoustic stimuli, habituation, and PPI were examined in 31 Chinese patients with first-episode, medication-naïve schizophrenia and 30 age- and sex-matched healthy Chinese controls. At the same day of startle testing, psychopathological symptoms of the patients were assessed with the Positive and Negative Syndrome Scale (PANSS).</p><p><b>RESULTS</b>Compared with healthy controls, patients exhibited the significant reduction in startle response and PPI deficits at 60 milliseconds (ms) intervals (PPI60, P < 0.05) but not at 30 or 120 ms intervals. Furthermore, there was a relatively strong correlation between PPI60 (P < 0.05) and scores of positive scale of PANSS in patients with schizophrenia.</p><p><b>CONCLUSION</b>Our findings confirmed impaired PPI in Chinese patients with schizophrenia and suggested that a relationship between sensorimotor gating deficits and clinical symptoms of patients with schizophrenia might exist.</p>

Neonatal ventral hippocampal lesion as a valid model of schizophrenia: evidence from sensory gating study / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>The neonatal ventral hippocampal lesion (NVHL) rat model has been proposed as an experimental model for schizophrenia. NVHL rats display impaired central nervous system (CNS) inhibition, which may lead to a phenomenon similar to P50 sensory gating deficits observed in schizophrenic patients. In this study, we investigated whether sensory gating deficits occurred in the NVHL rat as a model for schizophrenia.</p><p><b>METHODS</b>We created the NVHL rat model using ibotenate. The P20 and N40 were measured to assess sensory response and gating in NVHL and sham rats. Epidural electrodes recorded evoked potentials (EPs), from which latencies, amplitudes, difference scores (S1-S2), and gating ratios (S2/S1) were assessed.</p><p><b>RESULTS</b>Compared with sham controls, prolonged S1 N40 latency and decreased S2 N40 amplitude were detected in the NVHL group. In neither difference scores nor gating ratios, a significant difference was found between NVHL group and sham controls.</p><p><b>CONCLUSIONS</b>NVHL rats may be a valid animal model for schizophrenia. This strategy will be useful in future neurobiological studies investigating the etiology of schizophrenia.</p>

Childhood Attention Deficit in the Patients with Bipolar Disorder and CHRNA7 Gene Polymorphisms / 대한정신약물학회지

OBJECTIVE: Patients with bipolar disorder have attention deficit during even euthymic status. Bipolar disorder patients showed more childhood attention deficit and other ADHD like feature. Alpha 7 nicotinic receptor (CHRNA7) gene has been known to play roles in attention and sensory gating, and association between CHRNA7 gene and bipolar disorder has been reported. Therefore, we investigated a possible association between childhood attention deficit of bipolar disorder and CHRNA7 gene polymorphisms. METHODS: We included 122 patients with bipolar disorder (89 subjects of bipolar disorder type I, 33 subjects of bipolar disorder type II). Childhood attention deficit was measured by Wender Utah Rating Scale (WURS). Factor analysis was done for WURS to extract inattention factor from childhood ADHD like feature. Three factors were extracted: Impulsivity, Inattention, and Mood instability. All subjects were ethnically Korean. Genotyping was done for three intronic Single Nucleotide Polymorphism (SNPs) of CHRNA7 gene: rs2337506 (A/G), rs6494223 (C/T), and rs12916879 (A/G). Analysis of association was done by UNPHASED version 3.1.4, a free software for genetic statistics. RESULTS: Genetic association tests found no association between factor score of inattention and any SNP or combination of SNPs of CHRNA7. Positive association between WURS total score and SNP rs6494223 (p=0.043), factor score of impulsivity and SNP rs2337506 (p=0.038) as well as SNP rs6494223 (p=0.043) was revealed. These positive associations were survived after 1,000 permutation tests. Combination of SNPs association tests performed for total WURS and factor scores could not find any significant association. CONCLUSION: We could not find association between CHRNA7 gene and childhood attention deficit in bipolar disorder. However, we found CHRNA7 gene involved in childhood impulsivity of bipolar disorder, another ADHD like feature. Further studies with larger sample and denser polymorphisms are necessary to clarify genetic role of CHRNA7 in attention and impulsivity of bipolar disorder.

Prepulse Inhibition of Startle Response: Recent Advances in Human Studies of Psychiatric Disease

Prepulse inhibition (PPI) is considered to be one of the most promising neurophysiological indexes for translational research in psychiatry. Impairment of PPI has been reported in several psychiatric diseases, particularly schizophrenia, where PPI is considered a candidate intermediate phenotype (endophenotype) of the disease. Recent findings from a variety of research areas have provided important evidence regarding PPI impairment. Human brain imaging studies have demonstrated the involvement of the striatum, hippocampus, thalamus and frontal and parietal cortical regions in PPI. In addition, several genetic polymorphisms, including variations in the genes coding for Catechol O-methyltransferase, Neuregulin 1, nuclear factor kappa-B subunit 3 and serotonin-2A receptor were related to PPI; and these findings support PPI as a polygenetic trait that involves several neurotransmitter pathways. Early psychosis studies suggest that PPI disruption is present before the onset of psychosis. Also, discrepancy of PPI impairment between children and adults can be found in other psychiatric diseases, such as autistic spectrum disorders and posttraumatic stress disorder, and comprehensive investigation of startle response might contribute to understand the impairment of the neural circuitry in psychiatric diseases. Finally, recent studies with both Asian and Caucasian subjects indicate that patients with schizophrenia exhibit impaired PPI, and impaired sensorimotor gating might be a global common psychophysiological feature of schizophrenia. In conclusion, studies of PPI have successfully contributed to a better understanding of the fundamental neural mechanisms underlying sensorimotor gating and will certainly be most valuable in devising future approaches that aim to investigate the complex pathogenesis of psychiatric diseases.

Study on the P50 Auditory Evoked Potential in Mood Disorder Subjects / 신경정신의학

OBJECTIVES: Diminished suppression of the P50 response, a consistent finding in schizophrenia, has also been reported in patients with bipolar disorder. It is a promising endophenotype for schizophrenia, but its relationship to genetic liability in mood disorder is controversial. The present study investigated event-related brain potential (ERP) indices of auditory processing and sensory gating in mood disorder and subgroups of patients with bipolar disorder with or without a history of psychosis using the P50 dual-click procedure. METHODS: The P50 auditory evoked potential response to paired stimuli was measured in 77 subjects with mood disorder (58 with bipolar disorder and 19 with major depressive disorder) and 28 healthy controls. P50 parameters were compared between groups. RESULTS: P50 suppression in patients with mood disorder did not differ from that in the healthy subjects. Except for S1 latency, there were no significant differences in P50 parameters between the diagnosis groups. In patients with bipolar disorder, a history of psychosis made no difference to P50 parameters. CONCLUSION: P50 was not significantly impaired in patients with mood disorder. There has been much debate on the meaning of P50, and more studies including longitudinal within-subjects studies are warranted to clarify the meaning and mechanisms of P50.

A follow-up study on features of sensory gating P50 in treatment-resistant depression patients / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Depressive disorder is a well-known chronic, recurrent and disabling mental disease with high direct and indirect costs to society in both western and eastern cultures. Approximately 40% of depressed patients show only partial or no response to initial or even multiple antidepressant medications and are usually called treatment-resistant depression (TRD) patients. The present work was to measure the features of sensory gating (SG) P50 in TRD patients with the intent of understanding the characteristics of this disease.</p><p><b>METHODS</b>In 50 TRD patients, 39 non-treatment-resistant depression (NTRD) patients and 51 healthy controls (HC), auditory evoked potential P50 was measured using the conditioning/testing paradigm presented with auditory double clicks stimuli, and 36 TRD patients had repeated measurements after an 8-week venlafaxine treatment course.</p><p><b>RESULTS</b>All the depressive disorder patients, including the TRD and NTRD groups, showed an increased testing stimulus wave (S2-P50) amplitude compared to controls (P < 0.01 and P < 0.05), but there was no significant difference between the TRD and NTRD groups (P > 0.05). There were significant differences in the ratio of testing stimulus (S2) and conditioning stimulus (S1) (S2/S1) and in the value of 100 x (1 - S2/S1) among the three groups. Compared to the baseline, TRD patients had no significant changes of features and different expression of P50 after acute treatment (P > 0.05). Meanwhile, a statistically significant positive correlation of S2/S1 with the scores of the 17-item Hamilton Rating Scale for Depression (HAMD-17) (P < 0.01), and a significantly negative correlation of S1 - S2, 100 x (1 - S2/S1) with the scores of HAMD-17 (P < 0.01) were observed in the TRD patients' baseline measurement, but there was no correlation after venlafaxine treatment (P > 0.05).</p><p><b>CONCLUSIONS</b>Both the TRD and NTRD patients had obvious SG deficits, with a more severe deficit in TRD patients. Although, with a correlated relationship to the severity of depressive symptoms, SG P50 deficit might be suggested as a trait marker for TRD, and a combination of S2/S1 ratio, S1 - S2 and 100 x (1 - S2/S1), was recommended for electrophysiological measurement in TRD patients.</p>

P50 and Schizophrenia

One of the most widely recognized neurophysiologic endophenotypes for schizophrenia is deficient gating or inhibition of the P50 component of the auditory event-related potential(ERP). A deficit in P50 sensory gating refers to a dysfunction in the mechanism responsible for modulating the brain's sensitivity of filtering out irrelevant or background stimuli, perhaps as a result of dysfunction in inhibitory neural circuits. In this paper, we review the neuronal and genetic aspects as well as medication effects on P50 in schizophrenia.