Cat 'P300' and cholinergic septohippocampal neurons: depth recordings, lesions, and choline acetyltransferase immunohistochemistry

Event-related potential studies of outcome processing and feedback-guided learning

In order to control behavior in an adaptive manner the brain has to learn how some situations and actions predict positive or negative outcomes. During the last decade cognitive neuroscientists have shown that the brain is able to evaluate and learn from outcomes within a few hundred milliseconds of their occurrence. This research has been primarily focused on the feedback-related negativity (FRN) and the P3, two event-related potential (ERP) components that are elicited by outcomes. The FRN is a frontally distributed negative-polarity ERP component that typically reaches its maximal amplitude 250 ms after outcome presentation and tends to be larger for negative than for positive outcomes. The FRN has been associated with activity in the anterior cingulate cortex (ACC). The P3 (~300–600 ms) is a parietally distributed positive-polarity ERP component that tends to be larger for large magnitude than for small magnitude outcomes. The neural sources of the P3 are probably distributed over different regions of the cortex. This paper examines the theories that have been proposed to explain the functional role of these two ERP components during outcome processing. Special attention is paid to extant literature addressing how these ERP components are modulated by outcome valence (negative vs. positive), outcome magnitude (large vs. small), outcome probability (unlikely vs. likely), and behavioral adjustment. The literature offers few generalizable conclusions, but is beset with a number of inconsistencies across studies. This paper discusses the potential reasons for these inconsistencies and points out some challenges that probably will shape the field over the next decade.

Effects of sleep deprivation on neural functioning: an integrative review

Sleep deprivation has a broad variety of effects on human performance and neural functioning that manifest themselves at different levels of description. On a macroscopic level, sleep deprivation mainly affects executive functions, especially in novel tasks. Macroscopic and mesoscopic effects of sleep deprivation on brain activity include reduced cortical responsiveness to incoming stimuli, reflecting reduced attention. On a microscopic level, sleep deprivation is associated with increased levels of adenosine, a neuromodulator that has a general inhibitory effect on neural activity. The inhibition of cholinergic nuclei appears particularly relevant, as the associated decrease in cortical acetylcholine seems to cause effects of sleep deprivation on macroscopic brain activity. In general, however, the relationships between the neural effects of sleep deprivation across observation scales are poorly understood and uncovering these relationships should be a primary target in future research.

Decision making, the P3, and the locus coeruleus-norepinephrine system

Psychologists and neuroscientists have had a long-standing interest in the P3, a prominent component of the event-related brain potential. This review aims to integrate knowledge regarding the neural basis of the P3 and to elucidate its functional role in information processing. The authors review evidence suggesting that the P3 reflects phasic activity of the neuromodulatory locus coeruleus-norepinephrine (LC-NE) system. They discuss the P3 literature in the light of empirical findings and a recent theory regarding the information-processing function of the LC-NE phasic response. The theoretical framework emerging from this research synthesis suggests that the P3 reflects the response of the LC-NE system to the outcome of internal decision-making processes and the consequent effects of noradrenergic potentiation of information processing.

Abnormalities of P300 cortical current density in unmedicated depressed patients revealed by LORETA analysis of event-related potentials

The purpose of the present study was to investigate the neural substrates underlying event-related potential (ERP) abnormalities, with respect to the generators of the ERP components in depressed patients. Using an oddball paradigm, ERP from auditory stimuli were recorded from 22 unmedicated patients with current depressive episodes and compared with those from 22 age- and gender-matched normal controls. Cortical current densities of the N100 and P300 components were analyzed using low-resolution electromagnetic tomography (LORETA). Group differences in cortical current density were mapped on a 3-D cortex model. The results revealed that N100 cortical current densities did not differ between the two groups, while P300 cortical current densities were significantly lower in depressed patients over the bilateral temporal lobes, the left frontal region, and the right temporal-parietal area. Furthermore, the cortical area in which the group difference in P300 current density had been identified was remarkably larger over the right than the left hemisphere, thus supporting the hypothesis of right hemisphere dysfunction in depression.

Task-relevant late positive component in rats: is it related to hippocampal theta rhythm?

Long-latency components of event-related potentials (like the P300 or P3) correlate with the ability of subjects to detect and process unexpected, novel or task-relevant events. Task-relevant late positive components were recorded in the neocortex and hippocampus of rats performing an auditory discrimination task, similar to the "odd-ball" paradigm used in human experiments. Surface and depth electrodes were implanted in anaesthetized rats at frontal, temporal and anterior occipital neocortical regions and the hippocampus. After recovery from surgery rats were trained to discriminate two auditory signals, a frequent irrelevant tone and a rare tone related to water reward. In response to the task-relevant tone but not the irrelevant tone, P300-like late positive components (mean latency of 274 ms) were recorded throughout the surface of the neocortex. The largest amplitudes were found at the anterior occipital cortex situated above the hippocampal CA1 region. The amplitude of the task-relevant positive component increased further with cortical depth without reversing its polarity. An amplitude maximum was found in the CA1 region with a polarity reversal at the pyramidal cell layer and the largest negative amplitude in stratum radiatum. Power spectra of differences between responses evoked by task-relevant tones and those evoked by irrelevant tones revealed peaks in the theta range (4-12 Hz). It is suggested that the P300-like component in rats corresponds to a theta wave out of a burst of hippocampal theta cycles.

Intracerebral potentials to rare target and distractor auditory and visual stimuli. II. Medial, lateral and posterior temporal lobe

Event-related potentials were recorded from 1221 sites in the medial, lateral and posterior aspects of the temporal lobe in 39 patients. Depth electrodes were implanted for about 4 days in order to localize seizure origin prior to surgical treatment. Subjects received an auditory discrimination task with target and non-target rare stimuli. In some cases, the target, distracting and frequent tones were completely balanced across blocks for pitch and volume. Some subjects also received an analogous visual discrimination task, or auditory tasks in which the rare target event was the omission of a tone, or the repetition of a tone within a series of alternating tones. In some subjects, the same auditory stimuli were delivered but the patient ignored them while reading. A complex field was recorded, indicating multiple components with overlapping time-courses, task correlates and generators. Two general patterns could be distinguished on the basis of their waveforms, latencies and task correlates. In the temporal pole and some middle temporal, posterior parahippocampal and fusiform gyrus sites, a sharp triphasic negative-positive-negative waveform with peaks at about 220-320-420 msec was usually observed. This wave was of relatively small amplitude and diffuse, and seldom inverted in polarity. It was multimodal but most prominent to auditory stimuli, appeared to remain when the stimuli were ignored, and was not apparent to repeated words and faces. A second broad, often monophasic, waveform peaking at about 380 msec was generated in the hippocampus, a limited region of the superior temporal sulcus, and (by inference) in the anterobasal temporal lobe (possible rhinal cortex). This waveform was of large amplitude, often highly focal, and could invert over short distances. It was equal to visual and auditory stimuli, was greatly diminished when the stimuli were ignored, and was also evoked by repeating words and faces. Preceding this waveform was a non-modality-specific negativity, possibly generated in rhinal cortex, and a visual-specific negativity in inferotemporal cortex. The early triphasic pattern may embody a diffuse non-specific orienting response that is also reflected in the scalp P3a. The late monophasic pattern may embody the cognitive closure that is also reflected in the scalp P3b or late positive component.

Event-related potentials during an auditory discrimination task in rats

Event-related potentials (ERPs) during an auditory discrimination task were recorded both on the surface and at a depth of the auditory cortex in rats. Ten-kilohertz rare and 5-kHz frequent tones were used with the probabilities of 0.2 and 0.8. Lever pressing within 2 s, following the onset of the rare tone, was rewarded with food paste. In the performing condition, the surface ERPs for the rare tones consisted of P30, N50, P80, N130, and P290 components. Only the surface P30 and N50 showed a polarity reversal at the intracortical electrode, suggesting that these components are generated in the auditory cortex. The P290 was elicited in the performing condition but not in the resting condition, showing its task-relevancy. These results suggest that auditory ERPs similar to those in humans can be recorded in rats during an active discrimination task.