512 THE NEUROSCIENTIST Genealogy of the “Grandmother Cell”Copyright © 2002 Sage PublicationsISSN 1073-8584

The term “grandmother cell” refersto a neuron that would respond onlyto a specific, complex, and meaning-ful stimulus, that is, to a single per-cept or even a single concept. Asoriginally conceived, a grandmothercell was multimodal, but the termcame to be used mostly for repre-senting a visual percept. As we shallsee, the term arose because the firstsuch neuron was postulated to repre-sent a grandmother. There might bemany grandmother cells respondingto a specific stimulus, such as onegrandmother, but their responseproperties would be the same.Because of this redundancy, the lossof a grandmother cell or two mightnot result in loss of the percept.“Coding by grandmother cells” is atthe other extreme from “ensemble,”“coarse,” or “population” coding inwhich a grandmother or other stimu-lus is coded by the pattern of activity

over a group of neurons. In ensemblecoding, there are no “grandmothercells” that detect the unique collec-tion of features that characterize agrandmother. Rather, each memberof the ensemble responds somewhatdifferently, for example, to agranny’s wrinkles, white hair, or toseveral different old women; the cod-ing of a specific grandmother is doneby a unique pattern of activationacross the ensemble.

Starting in the early 1970s, theterm grandmother cell moved fromlaboratory jargon and jokes into neu-roscience journals and serious dis-cussions of the bases of pattern per-ception (e.g., Barlow 1972; Blake-more 1973; Anstis 1975; Frisby1980; Marr 1982; Churchland 1986).The term is now nearly ubiquitous inintroductory neuroscience and visiontextbooks, where it often plays therole of straw man or foil for a discus-sion of ensemble or coarse codingtheories of sensory representation(e.g., Cowey 1994; Gazzaniga andothers 1998; Rozenzweig and others1999). This essay considers the ori-gins of the term grandmother celland similar expressions and, morebriefly, the roots of ideas aboutensemble coding.

Jerry Lettvin and the Birth ofMother and GrandmotherCells

Jerry Lettvin originated the term“grandmother cell” around 1969(Barlow 1995) in his M.I.T. coursetitled “Biological Foundations forPerception and Knowledge.” Whendiscussing the problem of how neu-rons can represent individual objects,he told a (tall) tale of how the neuro-surgeon A. Akakhievitch had locateda group of brain cells that “respond-ed uniquely only to a mother . . .whether animate or stuffed, seenfrom before or behind, upside downor on a diagonal or offered by carica-ture, photograph or abstraction.” Atthis point, Lettvin introduced themother-obsessed character fromPhilip Roth’s (1969) novel Portnoy’sComplaint and Akakhievitch ablatedall of the mother cells in Portnoy’sbrain. As a result, Portnoy complete-ly lost the concept of his mother (seeBox 1). Akakhievitch then went on tothe study of grandmother cells.

From this origin, the term grand-mother cell seems to have spread soquickly that Horace Barlow in his1972 article “Single Units andSensation: A Neuron Doctrine forPerceptual Psychology” didn’t evenexplicitly define the term in criticiz-ing the idea and, in 1973, ColinBlakemore could write of the “greatdebate [that] has become known asthe question of the ‘grandmothercell.’ Do you really have a certainnerve cell for recognizing the con-catenation of features representingyour grandmother?”

Jerzy Konorski’s Gnostic Units

Although unknown to Lettvin, thegrandmother cell idea had actuallybeen set out in detail as a serious sci-entific proposal a few years earlierby the Polish neurophysiologist andneuropsychologist Jerzy Konorski inhis Integrative Activity of the Brain(1967), a wide-ranging set of specu-lations on the neurophysiology ofperception and learning (see Fig. 1and Box 2). His ideas on the organi-

Genealogy of the “Grandmother Cell”CHARLES G. GROSSDepartment of PsychologyPrinceton UniversityPrinceton, New Jersey

A “grandmother cell” is a hypothetical neuron that responds only to ahighly complex, specific, and meaningful stimulus, such as the imageof one’s grandmother. The term originated in a parable Jerry Lettvintold in 1967. A similar concept had been systematically developed afew years earlier by Jerzy Konorski who called such cells “gnostic”units. This essay discusses the origin, influence, and current status ofthese terms and of the alternative view that complex stimuli are rep-resented by the pattern of firing across ensembles of neurons. NEU-ROSCIENTIST 8(5):512–518, 2002. DOI: 10.1177/107385802237175

KEY WORDS Grandmother cell, gnostic cell, Konorski, visual coding, labeled line

� HISTORY OF NEUROSCIENCE

I thank G Berman, D Cha, DF Cooke, MFAGraziano, T Moore, and F Tong for theirdetailed comments. Supported by N.I.H. grantEY11347.

Address correspondence to: Charles G.Gross, Department of Psychology, PrincetonUniversity, Princeton, NJ 08544 (e-mail:cggross@princeton.edu).

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zation of the cerebral cortex in per-ception anticipated subsequent dis-coveries to an amazing degree.Konorski predicted the existence ofsingle neurons sensitive to complexstimuli such as faces, hands, emo-tional expressions, animate objects,locations, and so on (see Fig. 2). Hecalled them “gnostic” neurons, and

they were virtually identical to whatlater were called grandmother cells.He suggested that the gnostic neu-rons were organized into specificareas of the cerebral cortex hetermed “gnostic fields.” That is, hepredicted (correctly in many cases)the existence of areas of the cortexdevoted to the representations of

such things as faces, emotionalexpressions, places, and spatial rela-tions. Destruction of a gnostic fieldwould lead, he predicted, to whatwere later described as category-specific agnosias. Furthermore, helocalized many of these gnosticfields, such as the face field in theventral temporal cortex and the space

Box 1. Lettvin’s Story about Mother and Grandmother Cells (ca. 1969)

In the distant Ural mountains lives my second cousin, Akakhi Akakhievitch, a great if unknown neurosurgeon.Convinced that ideas are contained in specific cells, he had decided to find those concerned with a most primitiveand ubiquitous substance—mother. . . . And he located some 18,000 neurons that responded uniquely only to amother, however displayed, whether animate or stuffed, seen from before or behind, upside down or on a diagonal,or offered by caricature, photograph, or abstraction.

He had put the mass of data together and was preparing his paper, anticipating a Nobel prize, when into his officestaggered Portnoy, world-renowned for his Complaint. On hearing Portnoy’s story, he rubbed his hands with delightand led Portnoy to the operating table, assuring the mother-ridden schlep that shortly he would be rid of his prob-lem.

With great precision he ablated every one of the several thousand separate neurons and waited for Portnoy torecover. We must now conceive the interview in the recovery room.

“Portnoy?”“Yeah.”“You remember your mother?”“Huh?”(Akakhi Akakhievitch can scarcely restrain himself. Dare he take Portnoy with him to Stockholm?)“You remember your father?”“Oh, sure.”“Who was your father married to?”(Portnoy looks blank)“You remember a red dress that walked around the house with slippers under it?”“O Certainly.”“So who wore it?”(Blank)“You remember the blintzes you loved to eat every Thursday night?”“They were wonderful.”“So who cooked them?”(Blank)“You remember being screamed at for dallying with shikses?”“God, that was awful.”“So who did the screaming?”(Blank)And so it went. . . . It made no difference—Portnoy had no mother. “Mother” he could conceive—it was gener-

ic. “My mother” he could not—it was specific. . . . Akakhievitch then . . . went back to . . . “grandmother cells.”

This parable is abridged from a letter Lettvin sent Horace Barlow in 1995 (Barlow 1995). Much earlier, Barlow(1953) had described cells in the frog’s retina as “bug detectors,” but little notice had been taken. In the late 1950s,Lettvin and his colleagues at M.I.T. (Lettvin and others 1959) were studying these and other complex cells in thefrog, but again the mainstream neuroscience community had ignored their work. Thus, at a 1959 meeting on senso-ry communication at M.I.T., Barlow (respectable for other reasons by then) but not Lettvin had been invited; Barlowarranged for some of the participants to see experiments in Lettvin’s lab. Subsequently, a paper by Lettvin and oth-ers was added to the end of the meeting proceedings (Rosenblith 1961), and eventually Lettvin and others “on whatthe frog’s retina tells the frog’s brain” became well known. Presumably, Lettvin’s research on how the frog’s retinacodes complex stimuli (Lettvin and others 1959) was related to his story about mother and grandmother cells.

514 THE NEUROSCIENTIST Genealogy of the “Grandmother Cell”

field in the posterior parietal cortex(Fig. 3). Overall, these gnostic fieldsand their locations are remarkablysimilar to contemporary views of theputative functions of extra-striatevisual cortex based on monkey sin-gle neuron studies and human imag-ing experiments (e.g., Caramazza2000; Martin and others 2000).

At the time of their publication,there was nothing in the literaturelike Konorski’s ideas of highly spe-cialized perceptual neurons in mam-mals or of areas of the cortex devot-ed to the representations of particularclasses of visual stimuli. In retro-spect, however, it is possible to delin-eate the origins of Konorski’s specu-lations.

Konorski’s views of the neuralorganization of perception were asynthesis and extension of three linesof work in the decade before the pub-lication of his book. The first wasHubel and Wiesel’s (1962, 1965)demonstration of the hierarchicalprocessing of sensory information inthe geniculo-striate system. In theirschema, as one proceeds from center-surround to simple receptive fieldsand then to complex and then the(now revised) hypercomplex ones,both the selectivity of the cells andtheir ability to generalize across theretina increase. The possibility thatthis hierarchy of increasing stimu-lus specificity continues beyond V2and V3 was made explicit in their1965 article, which is repeatedlycited by Konorski. That article endsas follows:

How far such analysis can be car-ried is anyone’s guess, but it isclear that the transformationsoccurring in these three corticalareas [V1, V2 and V3] go only ashort way toward accounting forthe perception of shapes encoun-tered in everyday life. (p. 286)

A second line of inspiration forKonorski’s ideas was the research byKarl Pribram and his students, par-ticularly Mort Mishkin, on the cogni-tive effects of lesions on what wasthen called “association cortex” inmonkeys. From his close associationwith Hal Rosvold and Mishkin (bothcommented on earlier drafts of the

book), Konorski was well aware thatlesions of the inferior temporal cor-tex produced specific impairments invisual cognition in monkeys(Mishkin 1966) and that similarareas of association cortex existedfor audition and somesthesis. Today,at the annual meeting of the Societyfor Neuroscience, there are multiplesessions on inferior temporal cortexunder the general rubric of “Vision.”However, at that time most visualneurophysiologists had never heardof this area and did not realize that ithad visual functions, let alone that itsat at the top of a series of hierarchi-cally arranged extra-striate visualareas. Indeed, although V2 and V3had been described, no other extra-striate visual areas such as MT or V4were known until 1971 (Allman andKaas 1971). Citing Pribram andMishkin (1955), Konorski (1967)wrote:

In monkeys the gnostic visual areaseems to be localized in infer-otemporal cortex, as judged from

numerous experimental results inwhich ablations of this region pro-duced impairment of visual dis-crimination. (p. 123)

The third line of evidence for histheories of gnostic neurons and areascame from Konorski’s familiaritywith the various agnosias that followcortical lesions in humans from hisown clinical experience, from theWestern neuropsychological litera-ture, and from Luria’s work in theSoviet Union. He was aware of boththe symptomatic specificity of somecases of agnosia and their tendencyto be localizable. Furthermore,unlike most contemporary neuropsy-chologists and neurophysiologists,he was aware of the similarity ofhuman agnosias to the effects ofexperimental lesions in monkeys.For example, he directly relatedprosopagnosia or face agnosia afterventral temporal lesions in humansto the visual learning deficits inmonkeys after inferior temporallesions.

Fig. 1. Jerzy Konor-ski in front of theNencki Institute ofExperimental Bi-ology in Warsaw.(Photograph by theauthor in 1961.)

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In summary, Konorski’s propheticideas on gnostic neurons and gnosticfields came from a bold extension ofHubel and Weisel’s findings to accountfor specific cognitive effects of spe-cific lesions in monkeys and humans.

Konorski’s book received a longand laudatory review in Science

(Gross 1968). However, for at leastthe next decade virtually all the manycitations to the book were to the partsconcerned with learning rather thanperception; learning theory stilldominated American psychology. Asdescribed in the next section, theideas on gnostic neurons did influ-

ence one laboratory, namely, the lab-oratory that first reported (the pre-dicted) neurons in the IT cortex thatselectively respond to faces andhands.

In the last decade, gnostic cellshave begun to be commonly men-tioned in textbooks and in the vision

Fig. 2. “Particular cate-gories of visual stimulus-objects probably repre-sented in different gnosticfields” (Konorski 1967).

516 THE NEUROSCIENTIST Genealogy of the “Grandmother Cell”

and pattern recognition literature,usually as synonyms for grandmoth-er cells and usually in the context ofinferior temporal cortex cells.

The Discovery of Face andHand Selective Cells in theInferior Temporal Cortex

In the early 1970s, my colleaguesand I working at M.I.T. inCambridge, Massachusetts, reportedvisual neurons in the inferior tempo-ral cortex of the monkey that firedselectively to hands and faces (Grossand others 1969, 1972; Gross1998a). These observations wereprobably primed by our familiaritywith Konorski’s gnostic units as well

as the propinquity of Lettvin’s workon detectors in the frog’s eye (Lettvinand others 1959, 1961) also atM.I.T., Hubel and Weisel’s discover-ies on the hierarchical processing incats and monkeys across the river inBoston at Harvard Medical School,and local talk about grandmothercells. Starting 10 years later, thesefinding were replicated and extendedin a number of laboratories (e.g.,Perrett and others 1982; Rolls 1984;Yamane and others 1988) and wereoften viewed as evidence for grand-mother cells. Konorski (1974) him-self saw them as confirming hisideas of gnostic cells. For some time,these cells were the strongest evi-

dence for the existence of grand-mother/gnostic cells. However, therewas little good evidence for cellsfrom monkeys that are selective forother visual objects important orcommon for monkeys such as fruit,tree branches, monkey genitalia, orother features in their natural envi-ronments. Nonetheless, inferior tem-poral cells can be trained to showgreat specificity for arbitrary visualobjects, and these would seem to fitthe requirements of gnostic/grand-mother cells (e.g., Logothetis andSheinberg 1996; Tanaka 1996).Furthermore, there is now good evi-dence for cells in the human hip-pocampus that have highly selectiveresponses to gnostic categories(Gross 2000; Kreiman and others2000) including highly selectiveresponses to individual human faces(Kreiman and others 2001).

However, most of the reportedface-selective cells do not really fit avery strict criteria of grandmother/gnostic cells in representing a specif-ic percept, that is, a cell narrowlyselective for one face and only oneface across transformations of size,orientation, and color (Desimone1991; Gross 1992). Even the mostselective face cells usually also dis-charge, if more weakly, to a varietyof individual faces. Furthermore,face-selective cells often vary intheir responsiveness to differentaspects of faces, suggesting that theyform ensembles for the coarse or dis-tributed coding of faces rather thandetectors for specific faces. Thus, aspecific grandmother may be repre-sented by a specialized ensemble ofgrandmother or near grandmothercells (Desimone 1991; Gross 1992).

There are two reasons why themembers of face-coding ensemblesmay appear more specialized thanthe members of other stimulus-encoding ensembles, that is, whythere are many more face cells thanbanana cells. First, it is more crucialfor a monkey (or human) to differen-tiate among faces than among anyother categories of stimuli such asbananas. Second, faces are more sim-ilar to each other in their overallorganization and fine detail than anyother stimuli that a monkey must dis-criminate among. If there had been

Fig. 3. “Conceptual map of the human cerebral cortex.” A, anterior; P, posterior; L, lat-eral; M, medial. Projective fields are hatched; gnostic fields are plain. The modalityboundaries are thick lines. The arrows denote connections. The numbers are tentativecorrespondences with Brodman’s areas. The letters are gnostic fields shown in Fig. 2.V, visual analyzer; V-I (17); V-II (18); V-III (19); V-Sn, sign visual field (7b); V-MO, field forsmall manipulable objects (7b); V-VO, field for large objects (39); V-Sp, field for spatialrelations (39, right hemisphere); V-F, field for faces (37); V-AO, field for animated objects(37). A, auditory analyzer; A, projective auditory field (41,42); A-W, audio-verbal field (22);A-Sd, field for various sounds (22, right hemisphere); A-VO, field for human voices (21).The legends for the symbols for the Somesthetic (S) and Kinesthetic (K) fields have beenomitted. Ol, olfactory analyzer; E, emotional analyzer (Konorski 1967).

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strong selective pressure for a mon-key to distinguish individualbananas, it would probably haveensembles for doing so that weremade up of cells selective forbananas in general, but that showedgraded response to different charac-teristics of bananas.

Labeled Lines and Hierarchies

Two central characteristics of grand-mother/gnostic cells have a long his-tory. The first is that they are exam-ples of labeled line coding, and thesecond is that they are at the top of ahierarchy of increasing convergence.

Labeled line coding refers toactivity in a neuron coding a particu-lar stimulus property, such as lineorientation or a grandmother. Thisspecificity derives from the connec-

tions of the neuron, not from the pat-tern of the neuron’s firing as is thecase for various temporal codes suchas rate, latency, or phase locking.Perhaps the earliest notion of alabeled line was in Galen’s distinc-tion between sensory and motornerves in the second century (Gross1998a, 1998b). On the basis of hisexperience as physician to the gladi-atorial school in Pergamon, he real-ized that section of some nervesresults in a specific sensory loss andsection of others results in motor loss.He thought the distinction derivedfrom the connections of the nerves tospecific regions of the brain.

The first modern labeled line the-ory of vision was Thomas Young’strichromatic theory of color (Boring1950). Johannes Muller (1838/1965)then generalized this idea to all the

senses in his Doctrine of SpecificNerve Energies. In that doctrine, whena given nerve type (or nerve energy,in his terms) was excited, the sametype of experience is produced inde-pendent of the cause of the excitation.The first example of labeled linecoding by single neuron activity wasprobably Adrian and Matthews’(1927)finding that action potentials in agiven optic nerve fiber of the congereel signaled the photic stimulation ofa specific part of the eel’s retina.

Turning to the other property ofgrandmother cells, convergence, themost extreme example of neural con-vergence is William James’s conceptof a “pontifical cell” whose activityis identical to consciousness as inthis passage from his Principles ofPsychology (1890).

There is, however among the cellsone central or pontifical one towhich our consciousness isattached. But the events of all theother cells physically influencethis arch-cell; and through produc-ing their joint effects may be saidto ‘combine.’ (p. 179)

C. S. Sherrington in his classicMan on His Nature (1940) took upJames’s ideas that there might be“convergence . . . of the nervous sys-tem . . . onto one ultimate ‘pontificalnerve-cell.’” He then rejected pontif-ical cells in favor of an ensemble celltheory of consciousness as “a mil-lion-fold democracy whose each unitis a cell.”

Barlow (1972) thought that theproposal of grandmother cells wasinadequate because the multidimen-sional aspects of visual perceptscould not be represented by a singleindividual cell. Rather, he proposedthat a small number of cells would beneeded to represent a percept. Henamed such cells “cardinal” cellsbecause cardinals are lower in thehierarchy than popes and there aremore of them.

Concluding Comment

The idea that there might be conver-gence of neural input onto a singlecell, which would provide that cellwith the ability to represent a com-

Box 2. Jerzy Konorski (1903–1973)

Konorski’s (1967) speculations about gnostic cells came at the end of along and distinguished career studying the brain and behavior (Fonberg1974; Konorski 1974). As medical students in Warsaw, he and StefanMiller discovered that there was another type of conditioned reflex otherthan the one discovered by Pavlov, namely, one under the control of reward.They called it Type II to distinguish it from Pavlov’s which they called TypeI. Subsequently and independently, Skinner made this same distinction andKonorski and Miller’s Type II conditioning became known as operant orinstrumental conditioning.

After a few years as a psychiatrist, Konorski spent 2 years in Pavlov’slaboratory in Leningrad but never convinced the master that there reallywere two types of conditioned reflexes. Konorski then returned to Warsawand set up a conditioning laboratory in the Nencki Institute ofExperimental Biology. He also married and collaborated with Dr. LilianaLubinska who had studied neurophysiology in Paris and through herbecame familiar with Western and particularly Sherringtonian neurophys-iology. When the war started, Konorski was extraordinarily fortunate to beable to escape Poland. (His colleague Miller committed suicide when theNazis arrived.) His Russian friends got him appointed head of the famousprimate laboratory at Sukhumi on the Black Sea. The laboratory eventual-ly moved to Tbilisi as the Germans approached. It was still near the front,and Konorski had a great deal of experience treating head wounds in anearby army hospital. At the end of the war, he returned to Poland andplayed a major role in reconstructing Polish neuroscience as head of theDepartment of Neuro-physiology at the Nencki Institute.

In 1948, Cambridge University Press published his ConditionedReflexes and Neuron Organization, which was an attempt to bringPavlovian reflexology in line with Sherringtonian neurophysiology. In the1960s, there were close collaborative relations between Konorski’s labora-tory and the Laboratory of Neuropsychology at N.I.H. In addition to theconcepts of gnostic units and gnostic fields, Konorski’s Integrative Activityof the Brain (1967) contains many important and influential ideas aboutlearning and memory.

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plex and specific percept, seems tohave arisen independently severaltimes, first as the gnostic cells elabo-rated in detail by Konorski and thenas the grandmother cells derivingfrom Lettvin’s parable. Cells withproperties that are similar to those ofgnostic and grandmother cells havebeen found in both the inferior tem-poral cortex and the hippocampus.Grandmothers (and other complexobjects) may be represented byensembles of “grandmother” cells,which vary in their responses to dif-ferent aspects of the stimulus.Finally, contemporary human brainimaging studies have yielded spe-cialized regions of the cortex thatclosely resemble the gnostic fieldsproposed by Konorski.

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