Juha Arikoski

ERPs to pitch changes: a result of reduced responses to standard tones in rabbits.

Event-Related potentials (ERPs) were recorded in rabbits when pitch deviant tones occurred in a series of standard tones (oddball situation). In control recordings, the deviant tones were presented without the standard tones (deviant-alone situation). In the oddball situation, significant difference ERPs (deviant ERPs-standard ERPs) could be found in the hippocampal and cerebellar recordings but not in the visual cortex. All the ERPs to the deviant stimuli observed in the oddball situation were also present in the deviant-alone situation. The difference ERPs were therefore based on reduced responses to the standards. The results are discussed in the context of a mismatch negativity (MMN) in humans.

Hippocampal evoked potentials to pitch deviances in an auditory oddball situation in the rabbit: no human mismatch-like dependence on standard stimuli.

Hippocampal auditory evoked potentials (AEP) were recorded in 10 rabbits when pitch deviant tones occurred in a series of standard tones (oddball situation). In control recordings, deviant tones were presented without intervening standard tones (deviant-alone situation). All AEP deflections observed in the oddball situation were found also in the deviant-alone situation. Thus, it appeared that none of the AEP deflections to deviant tones in the oddball situation was specific to a memory trace of preceding standard tones. This observation was in contradiction to such a specificity of the mismatch negativity (MMN) found in humans. Instead, a connection to a neuronal orienting reaction interpretation was shown to be apparent. A need for additional control procedures revealing a contribution of neural orienting responses in animal MMN experiments is discussed.

Hippocampal event-related potentials to pitch deviances in an auditory oddball situation in the cat: Experiment I

Hippocampal event-related potentials (ERP) in the areas CA1, CA3, and dentate fascia (Df) were recorded in cats during an oddball situation when pitch deviant tones occurred in a series of standard tones. When difference waves were calculated by subtracting ERPs to the standard tones from those to the deviant tones, no clear N40d, corresponding to a cat analogue of the human mismatch negativity (MMN) observed in earlier studies, could be detected. Instead, a prominent later negativity (N130d) was observed. A possible extra-hippocampal source of the process reflected by the MMN-like negativity, and a relation between an orienting response (OR) and the N130d are discussed.

Multiple-unit responses to pitch changes in rabbits.

MULTIPLE-UNIT activity (MUA) was recorded from the hippocampus (Hc), the visual cortex (VCx) and the cerebellar cortex (CerCx) in rabbits when pitch deviant tones were presented in a series of standard tones (oddball situation) and when standard tones were absent (deviant-alone situation). Significant MMN-like responses (deviant responses minus standard responses in the oddball situation) occurred in He, reflecting a MUA increase to the standards and its decrease to the deviants. In accordance with parallel ERPs reported earlier, the MMN-like responses reflected responses only to different presentation frequencies of stimuli. Non-selectivity in the pitch of such responses in VCx and a lack of an effect of the different stimulus repetition frequencies on responses in CerCx resulted in absent MMN-like responses in both of these locations.

Behavioral and hippocampal evoked responses in an auditory oddball situation when an unconditioned stimulus is paired with deviant tones in the cat: Experiment II

Event-related potentials (ERP) in the areas CA1, CA3 and dentate fascia (Df) of the hippocampal formation were recorded during an oddball situation in the cat. A rewarding electrical stimulation of the lateral hypothalamus (US) was paired with deviant tones (2500 Hz) that occurred randomly in a series of the standard tones (2000 Hz) given to the left ear. In addition to developing orienting head movements to the side of the deviant tones, an increase in the amplitude of parallel hippocampal ERPs was observed. Both the behavioral and neural responses appeared not until a 50 ms latency range. Furthermore, time-amplitude characteristics of the ERPs corresponded to time-acceleration characteristics of the conditioned orienting head movements. The results are discussed in the context of a cat analogue of the human mismatch negativity (MMN) and a role of the hippocampal formation to model and predict the conditioned behavioral orienting responses.

Effects of lateralized US and CS presentations on conditioned head turning and bilateral cingulate cortex responses in cats

A lateralized tone conditioned stimulus (CS+) paired with a rewarding medial forebrain bundle (MFB) stimulation unconditioned stimulus (US) was presented to one ear of the cat, while the same tone was presented to the other ear alone (CS-). Specifically, the electrical stimulation of the MFB elicited a contralateral head turn as the unconditioned response (UR). Correspondingly, the CS+ was given to an ear contralateral to the direction of the UR. During the CS test session the cats oriented toward the tones, but these head movements habituated rapidly. During conditioning the cats developed stereotypical extended vigorous head turns to the CS+, with significantly greater acceleration and shorter onset latencies to the CS+ than to the CS-. Head turns in response to the CS+ were always ipsilateral to the tone, but responses to the CS- were in some cats ipsilateral and in most cats contralateral to the tone. Recordings of the slow potential responses showed a broad negative deflection in the cingulate cortex, with peaks at 140 and 250 ms. The amplitude of this negative potential to the CS+ was larger than that to the CS-, but no asymmetries were found between the hemispheres. The present behavioral paradigm is potentially useful for studying the neural basis of conditioned approach responses.

Effects of rewarding electrical stimulation of lateral hypothalamus on classical conditioning of the nictitating membrane response.

1. Adult New Zealand albino rabbits were prepared with chronic hypothalamic stimulating electrodes and hippocampal recording electrodes. 2. Rabbits were restrained and classically conditioned by a tone CS and an airpuff US either followed or preceded by a hypothalamic stimulation (HS). Control rabbits were conditioned without the HS. 3. It was found that HS following the CS facilitated both behavioral and hippocampal responses, while HS preceding the CS inhibited them. 4. Enhanced hippocampal learning-related unit firing to the CS may represent an early indication of conditioning before the behavioral activity produces any observable change.

Evidence of the origin of specific spontaneous head turns during intertrial intervals

Direction and the frequency of spontaneous head movements during the ITIs following forward and backward paired trials were compared to an acquisition of a conditioned orienting (alpha) response directed to the side of the tone source. The head movements were analyzed from video recordings using classification of head turns to preferred and to nonpreferred directions. The results showed a significant increase in the alpha responses during the forward paired conditioning to the preferred direction and rapid extinction during the subsequent backward conditioning sessions. Spontaneous head movements during the ITIs increased to the same preferred direction as the conditioned alpha responses. The results of this experiment suggest that the response initially elicited by the CS can later appear as “spontaneous,” instrumental behavior, the form and the nature of which is determined by the characteristics of the conditioned alpha response developing as a result of classical conditioning.