QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ramón, F. Articles by Bullock, T. H. Search for Related Content PubMed PubMed Citation Articles by Ramón, F. Articles by Bullock, T. H.

Event-related potentials in an invertebrate: crayfish emit ‘omitted stimulus potentials’

Fidel Ramón¹, Oscar H. Hernández² and Theodore H. Bullock^*,3

¹ División de Posgrado e Investigación, Facultad de Medicina, Universidad Nacional Autónoma de México, México, DF,
² Centro de Investigaciones en Enfermedades Tropicales, Universidad Autónoma de Campeche, Campeche, México and
³ Neurobiology Unit, Scripps Institution of Oceanography and Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093-0240, USA

View larger version (61K): [in a new window]   Fig. 1. Omitted stimulus potentials (OSPs) from crayfish. (A) Eight successive trials (single sweeps) from the protocerebrum, a locus that gives no visual evoked potentials (VEPs) and mainly spike bursts for OSPs. The last two flashes (arrows at bottom) of a 1 s train at 15 Hz are shown. Trials 1–4, from the top, with a low flash intensity of 1 (arbitrary units proportional to lumens); trials 5–8 at a high flash intensity of 16. (B) Simultaneous recording from the optic tract at a locus that shows slow waves larger than spikes, both VEP and OSP. Averages of the optic tract recordings 1–4 and 5–8, below, reveal the consistent slow negative wave approximately 40 ms wide and peaking at approximately 75 ms after the due-time of the first missing flash (vertical dashed lines). At some electrode loci, this wave is much more conspicuous than it is here. Note that the spike burst, without a slow wave, in the protocerebral locus (A) coincides with a spike burst in the optic tract (B). Both recordings were filtered to pass 1–2000 Hz. The recordings in A and B illustrate the robustness of the OSP and the small effect of the intensity of the conditioning stimulus train. (C) Effect of frequency of conditioning flashes. This recording was taken from the protocerebrum of another preparation and shows single sweeps after trains at different flash rates. Responses are aligned by the due-time of the first missing flash. Note the near constancy of the OSP latency, if measured from the due-time. At 3 Hz, no OSP is seen, and a single spike occurs in some trials at 4 Hz. At values above 15 Hz, some preparations continue to emit a burst at this time, whereas others do not. The constant latency from a given locus, within a given preparation, shown here, is the hallmark of the OSP. Its value varies with temperature and possibly with locus. (D) Recordings from another preparation showing the lack of effect of flash intensity over a range of 8:1 (same units as in A and B). Note the VEPs after each flash. These are of the small spike burst type, with long latency. (E) Effect of stimulus frequency on the amplitude of the OSP, estimated by the root-mean-square voltage (Vrms) during the 200 ms beginning with the due-time. The arrow marks the mean Vrms under the prevailing conditions, without stimulation. The increased Vrms beginning somewhat below 10 Hz is attributable mainly to the spike burst OSPs. Data are from three preparations, each shown by an individual symbol; values are means ± standard deviations (N=6).

View larger version (34K): [in a new window]   Fig. 2. The early, brief type of visual evoked potential (VEP). (A) Five successive single sweeps (the 21st to 25th of a series) with 1 s trains of 10 Hz flashes eliciting early biphasic VEPs following the stimulus artifact (variable because of the digitizing rate). Note the small spike burst type of omitted stimulus potential (OSP) approximately 140 ms after the due-time. (B) The same sweeps averaged after rectifying to avoid negative-going and positive-going spikes cancelling each other. The slow wave average OSP is thus the result of summing spikes in this case.

View larger version (32K): [in a new window]   Fig. 3. Variations among preparations. (A) Single sweeps from six animals. The loci in each case gave no visual evoked potential (VEP) but a good omitted stimulus potential (OSP), appearing as a spike burst, and all having a similar latency after the due-time. The OSP is seen whether the stimulus is in the middle of a train or at its end. (B) Some loci (here demonstrated from a seventh preparation) show slow waves overshadowing the spike bursts, in this case also giving VEPs. Four successive trains are shown, all at 15 Hz, with only the last four flashes in single sweeps.

View larger version (27K): [in a new window]   Fig. 4. Effect of conditioning time. (A) Short trains of stimuli. Root-mean-square voltage (Vrms) values (mean ± S.D., N=6) of 200 ms following the due-time of the first missing flash at the end of trains of various numbers of flashes at 10 Hz (squares and circles) and 15 Hz (asterisks). Since omitted stimulus potentials (OSPs) cannot confidently be identified after trains of only three or four flashes, Vrms values for such trains measure essentially the spontaneous activity. Values are higher for trains containing more than five flashes and reach a maximum at around eight flashes. In this preparation, the values increase again after 12–14 flashes. (B) Longer trains of stimuli. Trains of 9 Hz of various durations, showing only the last three flashes. This recording locus showed a late spike burst type of visual evoked potential (VEP) and a more vigorous OSP, essentially uninfluenced by the duration. The OSP after 30 s is anomalous.

View larger version (22K): [in a new window]   Fig. 5. Effect of time of day under natural laboratory light on root-mean-square voltage (Vrms) values (mean ± S.D. of 200 ms following the due-time of the first missing flash) at different times of the day. Values are averages of 5 days of recordings and show the diurnal fluctuation. After basal (spontaneous) values of approximately 300 µV, there is a clear increase in Vrms during daylight hours (06:00–18:00 h) with a return to basal levels after 20:00 h. A comparison with the light intensity values (shown in lx) in the experimental room averaging the same 5 days of recording (thin line) shows the extreme non-correspondence between omitted stimulus potential (OSP) and prevailing light. The skewness of the room light is due to the sun shining through the window near sunset.