Nonhuman Primate Model of Schizophrenia Using a Noninvasive EEG Method
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Nonhuman primate model of schizophrenia using a noninvasive EEG method Ricardo Gil-da-Costa1, Gene R. Stoner, Raynard Fung, and Thomas D. Albright1 Systems Neurobiology Laboratories, Salk Institute for Biological Studies, La Jolla, CA 92037 Contributed by Thomas D. Albright, July 5, 2013 (sent for review March 26, 2013) There is growing evidence that impaired sensory-processing sig- Given the homology of human and rhesus macaque brains nificantly contributes to the cognitive deficits found in schizo- (10), the development of a nonhuman primate (NHP) model of phrenia. For example, the mismatch negativity (MMN) and P3a schizophrenia holds great potential for understanding the un- event-related potentials (ERPs), neurophysiological indices of derlying cellular pathophysiologies and for exploring potential sensory and cognitive function, are reduced in schizophrenia treatments. Of particular importance is the development of meth- patients and may be used as biomarkers of the disease. In agree- ods that allow comparison of neurophysiological correlates of ment with glutamatergic theories of schizophrenia, NMDA antag- sensory and cognitive functions in NHPs and humans. To this onists, such as ketamine, elicit many symptoms of schizophrenia end, we developed a noninvasive electroencephalography (EEG) when administered to normal subjects, including reductions in the system that uses common recording hardware and analyses for MMN and the P3a. We sought to develop a nonhuman primate the two species. Our system uses a noninvasive EEG cap in (NHP) model of schizophrenia based on NMDA-receptor blockade NHPs, with electrode density identical to that used in humans. using subanesthetic administration of ketamine. This provided Our approach allows for the calculation of topographic voltage neurophysiological measures of sensory and cognitive function maps and localization of activity generators in the NHP brain. that were directly comparable to those recorded from humans. To determine the utility of our NHP EEG system, we recorded We first developed methods that allowed recording of ERPs from ERPs from humans (64-electrode array) (Fig. S1A) and NHPs humans and rhesus macaques and found homologous MMN and (22-electrode array) (Fig. S1B) during a passive auditory intensity P3a ERPs during an auditory oddball paradigm. We then investi- oddball paradigm. For both species, we established that ERPs gated the effect of ketamine on these ERPs in macaques. As found had timing and topographic distributions consistent with previous NEUROSCIENCE in humans with schizophrenia, as well as in normal subjects given reports, and source localization suggested homologous neural ketamine, we observed a significant decrease in amplitude of both generators. Next, we investigated the effect of transient admin- ERPs. Our findings suggest the potential of a pharmacologically istration of subanesthetic doses of ketamine on these components induced model of schizophrenia in NHPs that can pave the way in NHPs. These experiments revealed transient but selective for EEG-guided investigations into cellular mechanisms and thera- reductions of MMN and P3a components, which mimicked those pies. Furthermore, given the established link between these ERPs, previously seen in human subjects similarly treated with NMDAR the glutamatergic system, and deficits in other neuropsychiatric blockers. Most significantly, they also mimicked the chronic disorders, our model can be used to investigate a wide range of MMN and P3a reductions characteristic of schizophrenia. COGNITIVE SCIENCES PSYCHOLOGICAL AND pathologies. Our findings, thus, support the utility of this NHP EEG sys- tem, used in conjunction with a ketamine-administration model brain | psychiatry | neurology | monkey | medicine of schizophrenia, to assay sensory and cognitive deficits. Our approach can, thus, be used to facilitate understanding of neural chizophrenia is a multifaceted disorder that may originate circuit dysfunctions characteristic of schizophrenia. Additionally, fi from neuronal pathology in multiple brain systems (1). Current a wealth of previous evidence has shown a signi cant correlation S fi theories suggest that some of the sensory and cognitive symp- between behavioral de cits and modulations of the MMN and toms of schizophrenia may, at least partially, result from dysfunc- P3a ERPs in a variety of neurological and neuropsychiatric pa- thologies (e.g., Alzheimer’s disease, dementia, Parkinson dis- tion of the glutamate neurotransmitter system (2). In support of ease, affective disorders, and disorders of consciousness, etc.) (7, this theory, it has been found that acute subanesthetic doses of the – N 11 13). Thus, our approach may also enable exploration, at -methyl-D-aspartate receptor (NMDAR) antagonist ketamine neuronal and behavioral levels, of therapies targeted at this fi induces sensory and cognitive de cits akin to those experienced collection of pathologies. by schizophrenia patients, as well as decreases of the mismatch negativity (MMN) and P3 event-related potential (ERP) ampli- Results tudes (3). Comparison of MMN in Humans and Monkeys. The MMN is The MMN is thought to reflect preattentive detection of obtained by subtracting the ERP to the standard stimulus from a deviant stimulus (4), whereas the P3 is thought to reflect the the ERP to the deviant stimulus (see Materials and Methods). In redirection of attention to that deviant stimulus (5). In an odd- humans, the auditory MMN is well documented as a fronto- – ball paradigm, responses to deviant (or “oddball”) stimuli oc- central negative potential with a latency of 100 250 ms after curring among a sequence of standard stimuli are measured. The the onset of stimulus presentation and has sources in auditory MMN is obtained by subtracting the ERP to the standard stim- cortices and in the inferior frontal gyrus (14). Consistent with ulus from the ERP to the deviant stimulus, whereas the P3a is typically observed in the ERP to deviants. Schizophrenia patients appear less able to detect and direct Author contributions: R.G.-d.-C., G.R.S., R.F., and T.D.A. designed research; R.G.-d.-C. and R.F. performed research; R.G.-d.-C. and R.F. analyzed data; and R.G.-d.-C., G.R.S., R.F., and attention to novel stimuli than healthy controls (6). Consistent T.D.A. wrote the paper. with this behavioral deficit, the amplitudes of both the MMN (7) The authors declare no conflict of interest. and the P3 (8) have been found to be reduced in schizophrenia Freely available online through the PNAS open access option. patients, leading to the proposals that reduced MMN is a marker 1To whom correspondence may be addressed. E-mail: [email protected] or [email protected]. of progressive pathology (7) and that reductions in both MMN This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. and P3a are markers of vulnerability for this disorder (8, 9). 1073/pnas.1312264110/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1312264110 PNAS Early Edition | 1of6 Downloaded by guest on September 25, 2021 previous findings, our recordings revealed a human MMN oc- Low-resolution brain electromagnetic tomography (LORETA) curring 56–188 ms after stimulus onset, with a peak amplitude of was used to estimate MMN generators. In both species, the su- −1.83 μV at 104 ms [F(1,1259) = 97.12; P < 0.001; Fig. 1A; ad- perior temporal gyrus (STG) and frontal areas were estimated ditional information is in Tables S1 and S2] and a broad central- as primary neural generators (Fig. 1 B and D, lower images). scalp distribution [Fig. 1B, Upper; white arrow indicates the For humans, the frontal generators included the inferior frontal MMN (negative, blue) central-scalp distribution]. gyrus (IFG) and the superior frontal gyrus (SFG). For macaques, Unlike other previous studies that used epidural electrodes to the frontal generators included the rectus gyrus (RG) and the establish MMNs in NHPs (Macaca fascicularis) (15, 16), we use anterior cingulate gyrus (ACG). These data establish that com- high-density scalp electrodes, which enable scalp topographic parable MMNs can be recorded with high-density scalp electrodes voltage mapping and source localization. Javitt et al. reported from both species. Our findings, moreover, provide functional that MMN in the macaque had a peak latency of ∼80 ms (15). evidence that the neural generators of those ERPs may be ho- We found NHP MMN 48–120 ms after stimulus onset, with mologous in the two species. a peak amplitude of −1.62 μVat88ms[F(1,409) = 11.17; P < 0.001; Fig. 1C; additional information is in Tables S1 and S2], Comparison of P3a in Humans and Monkeys. The P3a emerges after and a central-scalp distribution [Fig. 1D, Upper; white arrow the MMN and has a latency of 200–500 ms in humans (17). We indicates the MMN (negative, blue) central-scalp distribution]. investigated the P3a in the averaged response to low and high We have labeled this ERP as “mMMN” (i.e., monkey MMN). deviants (see Materials and Methods for details). In humans, the A B µV -3 * -2 -1 0 1 2 3 -200 -100 0 100 200 300 400 500 ms C D µV -3 * -2 -1 0 1 2 3 -200 -100 0 100 200 300 400 500 ms Fig. 1. MMN in humans and NHPs. Left graphs show ERP plots of grand average from a central electrode (Cz) of five humans (A) and two NHP subjects (C). These graphs depict waveforms (averaged across low and high tones) from standard (blue line) and deviant (red line) conditions, as well as difference wave (black line). The blue shaded area identifies duration of the MMN [human: 56–190 m (peak amplitude, −1.83 μV at 104 ms; *P < 0.001); NHP: 48–120 ms (peak amplitude, −1.62 μV at 88 ms; *P < 0.001]. Human and monkey head icons identify species for results presented (they do not represent precise electrode placement or density). (B and D) Upper right images show scalp-voltage topographic maps, which reveal central negativity found in the difference wave for both species [human: time interval 56–188 ms (B); NHP: time interval 48–120 ms (D)] corresponding to the MMN [white arrow indicates MMN (negative, blue) central-scalp distribution].