Doc 0000173966

The image displays a digitally rendered graphic that serves as a title page or header for a collection of declassified documents. On the left side, a stylized illustration of a bank vault door is visible with blue lighting effects. The right side of the image features the text "THE BLACK VAULT" in a stylized font, followed by descriptive text explaining that the document originates from an online database of declassified government documents, specifically mentioning the MKULTRA/Mind Control Collection from the Central Intelligence Agency (CIA). A URL is also provided for the online collection. There are no photographs, handwritten annotations, official stamps, forms, diagrams, tables, redactions, or visual evidence of experimental procedures present in this graphic. \ ELECTRIC FISH Il\T\TESTIGATION l 1 Final Report . I I I i I i I i l i i \ Contract 8 March 1973 . I I I ~ i ILLUSTRATIONS figure Page 1 Mauthner cells 4 2 Electrorcccptors 6 3 Craninl.nerYCS of Elecb··>phorus 8 4 Microelcctrode amplifier 13 . 5 Microelcctrode amplifier: schematic diagrrun 13 6 Loss in -dB with increasing frequency 14 7 Loss in -dB with increasing repetition rate 15 i -8 Device for sharpening metal electrodes 17 I 9 Device for applying silver chloride 17 10 Potentiometric device 19 11 Device for measuring microelectrode resistance 19 11A Amplification factor, square wave 20 llB Amplification factor, sinusoidal wave 21 11C Recordings at different square wave 22 11D Recordings at different square wave 23 12 . Adjustable Lucite Tray 27 13 Instrumentation for Anaesthesia 27 14 Solution 1:10000 in water on Stcrnarchus nlhifrons 29 15 Sternnrchus nlbifrons 417 normal electrical activity 31 16 Stcrnarclms alhif1.·ons 4fr7 in anesthetic tricaine met1mne 31 sulfonate, 1 minute 17 Sternnrclms nlbifrons 4/7 in anesthetic tricnil•e methane 31 sulfonate, 2 minutes 18 Stcrnarclms alhifrons f!7 in :mcsthctic tricninc methane 31 sulfonate, 4 minutes • 19. Stc:.rnar~l}}_I_S. :1.11?!.!).:yJl!i #7 in anesthetic tricainc mclh::me 32 sulfonate, 5 minutes ?.0. Stcrnarchus nlb!fl.:9LI.~ rc<.:upcrnting, 5 minutes 32 Figure 21 Stcrnn.rchus albifrons recuperating, 8 minutes 32 22 Set-up for microelccb.·ode 32 23 Sternn.rchus albifrons No. 1 just before anaesthesia. 33 24 Sternn.rchus n.lbifrons No. 1 anaesthetized with thiopental sodium 33 (2 min.) 25 Sternn.rchus albifrons No. 1 anaesthetized with thiopental sodium 34 (13. 5 min.) 26 Sternarchus albHrons No. 1 anaesthetized with thiopental sodium 34 (37. 5 min.) 27 Sternarchus albifrons No. 2 in aquarium water 36 28 Sternarchus n.lbHrons No. 2 in MS-222, 10 minutes 36 29 Set-up for recording 38 ... . . . . 38 30 Close-up of the set-up for recording; 31 Stcrnarchus alhifrOltS after d-tubocurarinc injection 40 32 Ampullary, tonic electro receptors 40 33 Set-up for recording 41 3·1 Anaesthetized, curarized Sterna.rchus albifrons 41 35 Microelcctrode amplifier 43 3G Preamplifier 44 t 37 Synchronous tonic electrorcceptor recording 44 35 Nonsynchronous phasic elcctroreccptor recording 44 :l!l Gvmnn.rchus niloticus Cuv. #2 electric activity 44 ·1 (I Gvmnn.rdms niloticus Cuv. #3 electric activity 46 ·1 .. 1 . G\·nm:lrchus niloticus Cuv. #2 electric activity 46 ··- Gvmn:wchus niloticus Cuv. 412 electric activity 46 ... ., ... Gvrntl:lrclms niloticus Cuv. 4/3 electric activity 46 ..... • recording 44 :l!l Gvmnn.rchus niloticus Cuv. #2 electric activity 44 ·1 (I Gvmnn.rdms niloticus Cuv. #3 electric activity 46 ·1 .. 1 . G\·nm:lrchus niloticus Cuv. #2 electric activity 46 ··- Gvmn:wchus niloticus Cuv. 412 electric activity 46 ... ., ... Gvrntl:lrclms niloticus Cuv. 4/3 electric activity 46 ..... • • GYmn:lrclnts niloticns Cuv. 1r3 electric n.ctiYity 47 ";yn nn.rclms niloticns Cuv. f/3 electric activity 47 G\·mn:1.rchns niloticns, Cuv. (bn.by) - t~:msvcrsal cut 48 iv Figure Page -.' 47 G:f,!1marchus niloticus Cuv -air bl:Ldder and spinal cord 49 o 48 Gvmnarchus nHoticus Cuv - spin:Ll cord 49 . ..,._.,,: o ' 49 G:t,!!marchus niloticus Cuv. -brain 49 50 Delafield- Harris hemato"'-y~in staining method 50 51 MalaEterurus electricus Ji2 52 Malapterus clcctricus on the scale 53 53 DeYice for measuring the voltage 53 54 Discharges of the electric organ of Malapterurus electricus 54 55 Tonic, ampullary electroreceptor 56 56 Phasic, tuberous electroreceptor 57. 57 Tonic electroreceptor 59 .·58 Phasic electroreceptor 60 59 . Ampullary tonic electroreceptor 61 60 Stimulus recording 61 61 Tuberous phasic electroreccptor 61 62 Stimulus recording 61 63 Electrorcceptors of Gvmnarchus niloticus 62 64 Underwater pattern recoguition system 63 65 Recording from an anaesthetized, curarized 66 Sternarchus nlbifrons specimen 66 Microelectrode recording 66 67 Gymnarclm s nil oticus - photo 70 68 Gynmarclms nHoticus -placement of electric 71 transmitting and receiving organs 69 Fish Laboratory A 72. 70 Fish Laboratory B 72 .. - Table 1 Undcrwatc1· 1x1.t lcrn rcco~nition system · 55 SUMl\.IARY The elcch·ic or.gn.ns of Sternn.rclms nlhifrons, a South Americn.n fresh water weak electric fish, h.·wc been studied with emphasis on electroreceptors. The morpholog iral and physiological characteristics of electroreccptors, ampullnry a11d tuberous, a .. e discussed. Special instrumentation required for the role of these electroreceptors in pattern recognition has been developed. We have recorded with microelectrodes the autonomous autorhythmic electrical activ ity of the tonic asynchronous ampullary electrorcceptors of the South American weak fresh water electric fish Sternarchus albifrons. We have also recorded the electrical activity from the phasic tuberous elec1:roreceptors and of the synchronous ampullary electroreceptors of the. same electric fish, Sternarchus albifrons. Preliminary meas urements have been made. The electric discharge of l\.Ialapterurus electricus, an African fresh water strong electric fish, has been measured in and out of water. The autorhythmic activity of the ampullary electrorecepiors has been demonstrated. We obtained some specimens of the African weak fresh water electric fish Gymnarchus This page contains minimal visual content. It is primarily a text document with a title, subtitle, and date. A handwritten annotation in the lower right corner, "250", is circled. There is a vertical line drawn near the bottom center of the page. The document has a right edge that appears to be a scanned fold or binding line. The image is a black and white scanned document. It appears to be a table of contents or index for a document related to scientific experiments. The table lists "Figure" on the left and corresponding page numbers on the right, under the heading "Page". The text describes various scientific equipment and procedures, such as "Microelectrode amplifier", "Potentiometric device", and "Recordings at different square wave". There are no images, stamps, handwritten annotations, or redacted content visible on this page. Preliminary meas urements have been made. The electric discharge of l\.Ialapterurus electricus, an African fresh water strong electric fish, has been measured in and out of water. The autorhythmic activity of the ampullary electrorecepiors has been demonstrated. We obtained some specimens of the African weak fresh water electric fish Gymnarchus niloticns. Tl1ey are supposed to be the most sensitive of all the weak electric fishes k'"D.own: Together with two specimens about one foot long, \Ve received a number of baby Gvrnnarclms niloticus about two inches· long. The baby electric fish were in fected with a Saprolegnin. ftmgus nnd could not be saved, ~ut we fixed a number of them in buffered formaldehyde and one of them has been cut and mounted in paraffin for histological studies of the electric organs. Preliminn.ry measurements have been mn.de on the com.munication capability of adult G\'mn~rchus niloticus. = A study of the anesthetizing effect of tricaine-mcthancsnlfonatc (l\.18222 FINQUEL) on Stcrn:wdms :-tlhifrons has bcpn undertal\:cn by ploitlng time for the anesthesia and recovery for different specimens. vi A study of an anaesthetic which docs not affect the electric fish's electric organ pulse repetition rate is presented. Also, the effect of D-t11bocurarinc and the counter-effect of ncosti;;mine has been assessed for albifrons. Finally, some improvements in the micro Stcrn~rclms electrode recording instrumentation l1ave been made. The electric organs of Stcrnarchus a.lbifrons, a South American weak fresh water electric fish, have been studied with emphasis on electroreceptors. Recordings have been made from the asynchronous tonic as well as the synchronous tonic and the asynchronous phasic electroreccptors. The electroreceptors are part of the complex lateralis line system of the electric fishes. The other lateralis line system sensory receptors, lih:e mechanical receptors and displacement receptors, have been discussed as part of a general hybrid pattern recognition system of the fish. A passive hybrid underwater patter'n recognition simulation system has been advanced. A simulating model concept could be established for underwater pattern recognition through electric sensory receivers and electric fields. More histological work is needed to establish the rdationship between different elcctrorecept.ors and their innervation. This is also needed for a realistic simulation system of the underwater pattern recognition ability of the electric fishes . .. vii --- ·-------~~-~-~ - I. INTRODUCTION [none of our previous reports, we described the morphology of the electric organ 1 :>f Stcrna.rchus albifrons, a weak fresh water electric fish from South America. We mentioned a realistic simulation system of the underwater pattern recognition ability of the electric fishes . .. vii --- ·-------~~-~-~ - I. INTRODUCTION [none of our previous reports, we described the morphology of the electric organ 1 :>f Stcrna.rchus albifrons, a weak fresh water electric fish from South America. We mentioned that the electric transmitting organ of St01·narchus is derived from nervous tissue and not from modified muscle tissue like the majority of other elec tric fishes. Tlrls is making Stm11n.rchus different from other electric fishes: it has a very high signal rate and the sign::J.l is phase and amplitude modulated. The form, rate, and amplitude of the signals emitted by the electric fishes are as diverse as the forms and sizes of these fishes. Some of the weak signals are used to locate objects or animals in their environment, or for na\igation, species recog- 2 nition, and communication. The strong electric discharges serve for offense or 3 defense. Watanabe and Takeda investigated the effect of a-c current with a fre quency close to the electrical signal emitted by Eigenmannia. When the applied pulses came within:!:. 3 to 4 pps of the one emitted by Eigcnrnamua, the fish would change its rate by 4 to 5 pps in a dil~ection which increased tlie pps separation. In creasing the frequency of the applied a-c current inl pps increments caused the fish to shift its frequency correspondingly until it reached about 6 to 7 pps over its normal rate, when it :vould revert to its original rate. We obtained similar results in c.'.-pcriments with Stcrnarchus nlhifrons, but the applied a-c signal was within 0. 5 cycle of the signal of the fish, demonstrating how specific the applied signal must be to elicit a change in the Stcrnarchus signal rate: :!:. 0. 5 cycle is the range of sc lccthity of the fishes' electrical trru1smitting-receiving system. The fact that many fresh water and sea water electric fishes have never been studied may present some difncultics in obl1.inin:; special kincl<> of electric fishes, and their care may not be an c:1sy t!l.sk. There arc, howe\·cr, enough species to enable many c:-..-pcrimcnts. 1 Very little is known about the eleeirical activity of marine electric fishes except Torpedo and some rays. Narcinc Barzilicnsis is thu only known marine electric 4 fish lL.'l.Ving two different elect-ric organs. Bemtett stuilled the mode of operation of the electric organs of This page is a table of contents or figure list from a document. It lists figure numbers, descriptions of what each figure depicts, and corresponding page numbers. The descriptions mention experiments involving "Sternarchus albifrons" and "Gymnarchus niloticus" electroreceptor activity, some of which are related to anesthesia with thiopental sodium and d-tubocurarine injection. There are no photographs, handwritten annotations, or official stamps visible. The content appears to be purely textual data presented in a structured tabular format. enough species to enable many c:-..-pcrimcnts. 1 Very little is known about the eleeirical activity of marine electric fishes except Torpedo and some rays. Narcinc Barzilicnsis is thu only known marine electric 4 fish lL.'l.Ving two different elect-ric organs. Bemtett stuilled the mode of operation of the electric organs of Rain cglnntaria, a marine electric fish, and of the fresh water fishes Hypopomus and Stcrnopygus and compared them with Nnreinc, Mormy-rus, Stcatogenys, Gymnorhamphychtis, Maln.pterurus, Gymnotus carnpo, and Electro phorus elcctricus. The main objects of this study were the form, innervation, and physiology of the electroplates forming the electric transmitting organs.· The electroplates of. Hypopomus, Gymnotus carapo, Mnlaptcrurus, and some Mormyridae have the same surface area and produce spikes during discharge. The electroplates of Sten1opygus . and possibly Eigenmnnnia have iwo peculiar characteristics: there is a steady po- tential on which pulses are superimposed, and the resistance of the electroplates is similar at the peal{; or between the spil~es. The electroplates are of the type with a slow depolarization. In Hypopomus, 1\Ialaptcrurus, and of the Morm:yridae, the innervation of the 1~ost electric organs is tlu·ough st:Jll-:s. The stalks may serve to amplify depolarization until it would be able to invade the body of the electroplates. The discharge rate and du iy cycle have been compared for electric fishes like Sternopygus (rate= 50/sec) and Eigenmannia (rate= 280/sec) with the Sternarchidae (ma.~. 1500/sec}. Compared with mammalian central nervous systems, peak fre quencies of the electric org·ans are not greatly different. The Ibnshaw cell can 5 discharge impulses at a rate of 1400/sec , and neurons in the sensory path some- ' 6 limes produce bursts at a rate of about 1000/sec. ll1 an examination of discharge ·pattern and organ fw1~tion studies, it was noted that 7 Gnmdfcst defined two groups of electric fishes: those that emit signals at a cons~wt 2 rate, and those that emit pulses with a variable rate. For example, Gymn:trchus, Stcrnopyg;us, and Eir;enmamrln are in the consta.nt rate group; Electro-phorus, GIU'lthonemus pctersii, Steatogcnys, and Hypopomus belong to the variable rate 4 p·oup. Bellllett did not make any connection between the electric fishes' electrical . systems, their environment, and their belmvior. No one investigated their evolu- tion, very little is known about their mating or birthplace, and no one has reported the breeding of electric fishes confined in water tanks. Sternnrchus albifrons also has two kinds of electrorecep1Drs: tonic and The image is a scanned page from a document that appears to be a table of contents or index. It is primarily text-based, listing figures and their corresponding page numbers. There are no photographs, handwritten annotations, stamps, forms, diagrams, or organizational charts visible. The content is structured as a two-column table. There is no visible evidence of experimental procedures, equipment, or facilities. the electric fishes' electrical . systems, their environment, and their belmvior. No one investigated their evolu- tion, very little is known about their mating or birthplace, and no one has reported the breeding of electric fishes confined in water tanks. Sternnrchus albifrons also has two kinds of electrorecep1Drs: tonic and phasic, and they are autorhythmic. These electr01•eceptors are sensitive to movement and di rection. The phasic electroreceptors seem to be related to informatim regarding - . . movement of objects near or around the fish. Accepting the principle of pacemaker activity in the brain, it seems that there are only a reduced number of command nuclei acting on the electric transmitting organ. It is also reasonable to assume that electrically mediated positive feedback must be present; chemically mediated transmission would be too slow for the repetition rate of transmission which can attain under certain circumstances over 1, 300. Mautlmer cells of lower vertebrates (Figure 1) can be considered single cells 8 9 command system for the, axial musculature on either side of the body ' • In the hacketfish each Mauthner fiber activates the muscles depressings both pectoral fins and these cells thus constitute a bilateral command system for the depressor 11 muscles~0' For e:o...-plaining the pacemakers action of the command nuclei in the brain of the mormyrid electric fishes a mutual excitation with positive feedbaci~ has been proposed. This theory would not work for the Mauthner cells. There is a crossed inhibition between the 1\!autl~er cells in the brain of the goldfish and it could equally be effective in an electric organ system. There is a requirement of high speed - . . . "'f traTtsmiss!on in synchronized systems like many of the electric transmitting organs. This has been useful in predicting site!'> where transmission has been 3 -------------·--····--···------- .. ijr 1~1 Nih-<cird G.ci h:,i ~ ft.<.(Tf'~ ;-;~ -.:.<Oni tbj Figure 1. (a) Schematic drawings of tRe location of the Mauthner cells (from Furulmwa and Furshpan ) (b) The principal circuitry involved in 1\lattthner reflex (only the \'111-th nerve conne~tions <Uld collatcrals deriving from the excited 1\lautlmcr cell arc shown). 4 electrically mediated. Positive feedback may be a "sine qua non" requirement for the pacemaker nuclei of electric transmitting organs. There is proof of positive feed- . 12 13 back in the mutual inhibition system of arthropod compound eyes ' • Th neural systems controlling electric organs have provided The document page contains a typed summary of research related to electric fish and their electroreceptors. It includes scientific terminology and mentions specific species for study, such as *Sternarchus albifrons*, *Malapterurus electricus*, and *Gymnarchus niloticus*. There are no photographs, handwritten annotations, stamps, forms, diagrams, tables, or redactions visible on this page. The content focuses solely on presenting research findings in a textual format. The page is primarily text, with some scattered dark spots that resemble ink blots or dust. There are no photographs, handwritten annotations, diagrams, tables, or forms. The text is formatted into paragraphs, discussing electroreceptors in fish and potential simulation systems. At the bottom right corner, the Roman numeral "vii" appears, suggesting it is the seventh page of a document. There is also a thin horizontal line at the very bottom with some indecipherable markings beneath it. shown). 4 electrically mediated. Positive feedback may be a "sine qua non" requirement for the pacemaker nuclei of electric transmitting organs. There is proof of positive feed- . 12 13 back in the mutual inhibition system of arthropod compound eyes ' • Th neural systems controlling electric organs have provided a large number of ~ ex:.mples of electrically mediated transmission, which meets the functional require mtnt for rapid communication between cells. This mode of transmission also proves to be able to mediate many functions often considered as restricted to chemically mediated transmission. The correlation between morphologically close apposition and electrotonic coupling was considerably strengthened by the work on electro motor systems. This correlation helps to validate morphological identification of electrical transmission in other systems where electrophysiological analysis is not so simple. It is not known whether there is any relevance to higher systems of the organizational principles deduced from electric organ systems. The next level of analysis of the electric organ systems may be no easier than the study of less specialized systems that are of more general interest. Some knowledge is being obtained of afferent pathways from electroreceptors in weakly electric fish which have important inputs to the electric organ control system. Both operant and respondent conditioning of the control system can be obtained and conditioned response latency can be very short. It is not unreasonable that the complete neural pathway of the conditioned response could be obt~ined in these cases. The central connections are still minimally explored; one knows what goes in and one can go from the electric organ several synapses antidromically. The rewards for filling in the gap would be great, :md prospects for at least some progress are bright. In Stcrnarchus albifr~ electrorcceptors are distributed over the entire body. The r!~sic tuberous. receptors are v~ry numerous as compared with the tonic ampullary receptors (Fi.gurc 2). The density of receptors is greatest in the head region and 5 ---- -.--- ··-~-··--- ---·--··------·~-------- -.-.,.--...- ---·~··-.-.,._..-----~--·------.,"·-"' _____, . ______ ._.-.. ----_,_,__.,._..,.._,.."'-·~·-"'. • z•. ..._•. -~ l Tonic, Ampullary Receptor i\ fv \ ..;. ...._/v _ J J ~. ........- /'./'---- ~ external, internal, and skin resistances Fi~n·c 2. ~natomical di:tg;t·:tms and cqui\·alcnt circuits of c !cclrorc<.~eptors in frcsh \\'atC'r electric fish: (:t) tonic, ampu1lat·y receptor and {b) phask, -~uhC'rous rcccptor. Diagrams arc Rlhl\\'11 with the external medium to ·the top. The skin and wall of l'Cl'Cptor caYil ios The page contains text from a document, likely a scientific paper or report, regarding electric fish. There are no photographs, stamps, handwritten annotations, or forms visible. The text itself discusses the morphology and signal transmission of electric fish, specifically mentioning the *Sternarchus albifrons* species. There are also superscript numbers, indicating footnotes or citations within the text. The visual content is solely the printed text on a plain white background. ........- /'./'---- ~ external, internal, and skin resistances Fi~n·c 2. ~natomical di:tg;t·:tms and cqui\·alcnt circuits of c !cclrorc<.~eptors in frcsh \\'atC'r electric fish: (:t) tonic, ampu1lat·y receptor and {b) phask, -~uhC'rous rcccptor. Diagrams arc Rlhl\\'11 with the external medium to ·the top. The skin and wall of l'Cl'Cptor caYil ios arc sho\\11 in cross S<. clion as lim's. The opcnin~ to tltC' exterior of phasic rc<·t•ptot· c:wity is shown ns oecludcd by a po1·ous mass. The ncr\'c fibers imwn·atin~ r(•ccpfot· <"~·Jis arc indicated. .. ·;: falls gradually toward the posterior end. There arc minor morphological subdivisions within the phasic and the tonic receptors, but no physiological correlations have been . d14, 15, 1G yet ob tame . In Figure 2 the equivalent circuits of tonic, ampullary and phasic, tuberous organs is sh0\\11. Cross sections through the receptors are shown with the ext~rnal medium to the top. The skin and wa~ls of the receptor cavities are represented by lines, innervation of the receptor cells is indicated. The electroreceptors over the entire body are innervated by the anterior lateral line nerves, a large branch of which runs posteriorly to join the posterior lateral line 17 nerve just behind the head (Figure 3). The posterior lateral line contains only . . . 18 19 mechanoreceptive f1bers which come from free neuromasts and canal organs ' · • The receptor cells of tonic receptors appear to behave very nearly like linear elements; that is, their membranes have fixed internal potentials, resistances, and capacitances. They are, in a sense, electrically inexcitable, and they differ markedly in this respect from phasic receptor cells. There is evidence for chemically mediated 20 transmissions at tonic receptors of gvnmotids The morphological characteristics of the snyapse are those typical of chemically mediated transmission. A strong brief anodal stimulus produces an evoked response long outlasting the stimulus. Then there is a synaptic delay between the initiation of the impulse and the nerve impulse (between 0. 5 and 1. 5 msec). Mormvrid tonic receptors are similar to those of gymnoticls and Gymnn.rchus nilotieu s tonic receptors are morphologically similar, 21 but they were not physiologically studied • The relationship between the different electroreceptors of Sternarchus albifrons in pattern recognition has not as yet been studied. The pres.cnt study developed special instrumentation required for in':estign.ting the roles of. these clectroreccptors in pattern recognition and obtained preliminary measurements of electrical discharges from 1\In.lapterurus clC'c:lricus This page is a research document, likely a scientific paper, focusing on electric fish and their electrical activity. It contains no photographs, diagrams, forms, or stamps. The text is dense, with several scientific names of fish underlined. There are a few small, sparse handwritten annotations, and the only significant visual element is the printed text itself, presented in standard paragraph format. The document appears to be a factual, scientific excerpt with no visual indication of experimental procedures or facilities. were not physiologically studied • The relationship between the different electroreceptors of Sternarchus albifrons in pattern recognition has not as yet been studied. The pres.cnt study developed special instrumentation required for in':estign.ting the roles of. these clectroreccptors in pattern recognition and obtained preliminary measurements of electrical discharges from 1\In.lapterurus clC'c:lricus in and out of water. 7 . /~4\ t. ___ _ ----. .... _ ......... .. ... • 1 ~ I I f I ; ~ ; ' ,. ' Figure 3." Hori7.ont:t1 projection of the crani:tl ncrYes of Electrophorus. Note the small size of the brain. Some ncrYes arc indicated by .ilic cot~ responding nurnbcrs. L.A. ncrYus Iatcralis :mtcrior; f· . ··~ ,.. · . Ll' ncrYus latcr:dis postcrio1·; Oc-Sp, occipito-spinalis ner\'e. s ---------------·--·--·----~------ : ~- '~ In our e~l)Crimcnts, tho perception of oh]ects by weal~ electric fishes by way of the discharge of their electric organs (transmitting and receiving) has beet~ demonstrated. 22 tl~<tt Other authors have shown weak electric fishes· cn.n be trained to distinguish between conducting and nonconducting objects placed in the water. For tbis Idnd of reception, two possible modes of action at the level of specific re- . 22 ceptors could be proposed: the "pulse-frequency-modulation" and tho "pulse- phase-modulation"23. According to the first hypothesis, sensory information should . . be conveyed by the frequency of the sensory impulses dependent on t11c pulse of the electric organ discharge whereas, according to tl1e second hypothesis, t11o time re lation (the phase) between the electric discharge and the following scn~::ory impulse would play an important role for the sensory coding. From our experiments with Sternarchus rubifrons, a South American weak fresl1 water electric fi::;h, we con ~luded that apparently neither of the above proposed mechanisms arc operating in this fish. The intensity of current flowing at the level of the receptor is coded by the munher of impulses elicited by each electric org::u1 discharge. Str!rnnrchus albifrons can discharge at rates l1igher th:m 1000 per second and tho fZ0nsory impulses of the receptors can follow their dis.9harge rate. 24 25 In some morm:;'1..·ids and gymnotids , however, modulation of the r0lation electric organ pulse-sensory impulse may be used for eloctrosensory coding. In mormyrids, also, the change in intensity of the electric field may be coded by char.~ing tile latency between the electTic organ pulse and the sensory receptors' impulse. In mormyrids, it may att.1.in values up to 9 This page contains only text, with no images, stamps, handwriting, forms, or diagrams. The text is printed and appears to be from a scientific document. There are no redactions or visual evidence of experimental procedures. of the r0lation electric organ pulse-sensory impulse may be used for eloctrosensory coding. In mormyrids, also, the change in intensity of the electric field may be coded by char.~ing tile latency between the electTic organ pulse and the sensory receptors' impulse. In mormyrids, it may att.1.in values up to 9 msoc, whereas in gynmotids it has been fr.~·;r.d not to exceed 1-2 msoc. It has been previously mentioned that in Stcrnarchus n.lbifrons tho ck';:rorcceptors arc distributed over tho entire body of the fish and that the ampullar:; ._,._,:rJc receptors arc more numerous than tho tuberous phasic receptors. We rccorde:r: ·.;-:<.:n tho auto rhythmic clcctric~l activity of the nonsynclu·onous t011ic, ~mpulln.ry e:: ·..;-:;~rorcccplors of StCl,larchus nlbifrons. The impulses were in'Cb'lihtr around a rcr.r;. ·-~ :!o:1 rate of .. -< .-:J. : between 100 and 300, with an amplitude of arotmd 2. 5 mV. The impulse duration was around 200 microseconds. There nrc other types of tonic receptors which are synchronous. The phasic W1i ts are nonsyuchronous. The nonsynchronous tonic receptors seem to rcnct indcp::mdently from the trans mitting electric organ. TI1ey react to any objects brought near the fish at a certain range. The recording shown in our fino.I report is made from such type of receptors. As pre'Viously nientioned, some fresh water weak electric fishes have the ability of percei'Ving objects, their movement: and direction, and also to determine some cllar acteristics of these objects (such as conductivity). For tllis underwater pattern recognition, th