Von Economo Neurons in Indian Green Ring Neck Parrot (Psittacula Krameri): Possible Role in Vocal Learning

Research Article

Austin J Anat. 2017; 4(3): 1072.

Von Economo Neurons in Indian Green Ring Neck Parrot (Psittacula Krameri): Possible Role in Vocal Learning

Shubha S* and Sudhi S

¹Department of Zoology & Applied Aquaculture, Kashi Naresh Government Post Graduate College, India

²Department of Zoology & Applied Aquaculture, Barkatullaha University, India

*Corresponding author: Shubha S, Department of Zoology & Applied Aquaculture, Kashi Naresh Government Post Graduate College, Bhadohi, India

Received: April 14, 2017; Accepted: June 07, 2017; Published: June 14, 2017


Only a few vertebrates communicate acoustically, notably the three birds’ group - songbirds, hummingbirds, and parrots; and some mammals – cetaceans, bats, elephants, seals, and hominids are able to produce elaborate patterns of vocalization. Vocal learning and Imitation is a rare trait and one of the highest forms of social learning. Here detailed anatomical investigation of the brain of Indian parrot - an exclusive imitator, reveal that brain wiring of parrot is unique with specialized cells and lacking multilayered cortical structure. We encounter an unusual neuronal type, known as Von Economo Neurons (VENs) in parrot – those have been noticed to date only in a few groups of mammals like humans, elephants, cetaceans, pinnipeds, and a few primates. Almost all are vocal learners. Functionally these neurons are associated with intelligence, cognition, emotion, facial expression as well as autonomic visceral, olfactory and gustatory functions. The presence of VENs in vocal counterparts of parrot pallium especially in the nidopallium caudolaterale (callopallial anterior region), lemnopallial region - the dorsolateral corticoid area (CDL), and in Arcopallium, indicate that parrot brain is restricted with compact nuclei and diversity of neural subtypes. Except VENs, Fork neurons and enveloping neurons have also been noticed in these regions. Strikingly similar Neuroarchitecture of vocal control areas of parrot brain to upper layer of mammalian neocortex provide clues of involvement of these neurons in the processing of vocal communication and imitation. These findings are important to understand the common blueprint of brain wiring of high-level cognition during evolution and related neurodegenerative disorders.

Keywords: Fork neuron; Lateral pallium; Indian parrot; Vocal learning; Neuroarchitecture; Von economo neuron


Human language is a unique and complex phenomenon, of the combination of imitation, memory, thought, emotions, logic, syntax, reasoning etc, and requires an enormous amount of brain resource. These resources are necessary to assemble information, syntactic constructions of thousands of words and their interconnections. The neuronal components of all these brain resources are still not fully known. Some of them we can definitely find with animal communication. Vocal production learning and imitation (the substrate for human language) one of the highest forms of social learning, is a rare and critical trait appears to have evolved independently in restricted groups of birds and mammals. Certain distantly related groups of large brain mammals –humans, cetaceans [1], elephants [2,3] harbor seals [4], dolphins [4,5] and pinnipeds (walrus) [6] can learn to produce elaborate patterns of vocalizations and can grasp most the meaning of sound. This rare ability is also reported dramatically in some small brain mammals, such as pygmy hippopotamus, manatee [7], ring- tailed lemur [8] pig [9,10], Deer [11], macaque monkey [12], rock hyrax [13], goat [14], and cattle [15]. In mice (Musmusculus) varying level of complex calls have been noticed [16]. Vocal communication in bats has also been studied extensively [17].

A few bird groups- songbirds, hummingbirds, and parrots also have the ability to imitate sounds. The Parrot family other than humans, cetaceans, and elephants etc. has shown the capability of extensive and rich vocal imitation [18-20] that can imitate human speech without training or an obvious reward [21]. Moreover, parrots are also found having emotions, cognition and social intelligence [22].

Surprisingly large, spindle -shaped bipolar projection neurons the Von Economo Neurons (VENs) are discovered in the layer V of the Anterior Cingulate Cortex (ACC) and Fronto Insular cortex (FI) of same groups of animals- humans, great apes [23-26], cetaceans [27- 28] elephants [29], in anterior insula of macaque monkey [30-11], pygmy hippopotamus, the Atlantic walrus, Florida manatee, zebra, horse pig, [31-32], rock hyrax, and white- tailed deer [33]. Almost all these species have shown capabilities of vocal production learning. VENs are considered as unique neurons due to their confined presence, restricted location, and specific morphology. Functionally VENs in great apes has been associated with social cognition and selfawareness, in cetaceans and elephants these cells have been correlated with brain size and the ‘social brain’. The speculation that VENs are recently emerged specialization to facilitate rapid information processing in large size brain is also not seemingly true as these cells have also been reported in comparatively smaller brain, like- lemurs [34] pygmy hippopotamus [31-32], the Florida manatee, [35] as well as macaque monkey [30,11].

The emergence and localization of high density of these specialized neurons in Anterior Insula (AI), and ACC of humans suggests their role in the development of intelligent behavior [24], integration of emotions, facial expression, [36], social conduct [37], as well as regulation of autonomic visceral, olfactory, and gustatory functions [38] with highly uncertain situations [39], salience evaluation [40] and self- regulation [36,41]. The vulnerability of VENs in pathological Dementia (Social behavior deficit), autism (language deficit), [36] and neuropsychiatric and neurodegenerative disorder (Alzheimer’s) suggest their role in social behavior [37]. Certain forms of human dementia that involve loss of self-awareness, perspective talking, and empathy are also correlated with loss of these neurons [38-42]. Altered morphology, number and function of VENs in autism spectrum disorder [43] propose their role in complex social-emotional functions, and complicated cognition such as selfawareness, judgment and emotions. Thus, the emergence of VENs is of enormous consequence in human brain evolution.

Recently ubiquitous localization of VENs in many neocortical regions of pygmy hippopotamus and their presence in layer II of the frontopolar cortex.

Artiodactyls especially domesticated pig, sheep, cow, and whitetailed deer [34] also abandoned the speculation that these neurons are the specialization of only hominids and large mammals.

Taken together, these interpretations imply that the VENs functions have been associated with their presence in functionally distinct areas of the human brain. But the presence of these cells in the diverse group of animals emphasized the need to understand the function of these cells in different animals.

The number and arrangement of VENs have also been found to be proportionately related to the complexity of social interactions of the hominid species. Socially humans and bonobos are the most interactive in which VENs are almost clustered and numerically high. The number is the highest in humans than in gorillas, and least in orangutans which had only a few isolated VENs [23]. On the basis of the review, we have reason to speculate that vocal production learning is the common function in all VENs containing animals and these neurons may also be present in those bird taxa that are known to produce phonological syntax naturally. Parrots’ oratory skill and their emotional make-up compel to think, that their neuronal components may provide some special clues, to understand the process of evolution of vocal production learning and language. Until now, it is also not clear what type of neuroarchitecture is responsible for such complex cognitive behavior and social intelligence in birds, while the high brain- body ratio, brain circuitry and connectivity of birds and mammals are found remarkably similar [19,44]. Comparative study of neural groupings characteristic of bird telencephalon and the laminar arrangement of neurons found in the mammalian neocortex is necessary to determine the structural homologous relationship between bird pallium and mammalian neocortex.

The present paper is an attempt to explore in much greater detail the possible shared neural features of birds and mammals that may generate such higher levels of consciousness, and also determine whether a morphologically similar neuroarchitecture is present in parrots which display complex intelligent behavior similar to intelligent mammals. This study also explicates that the large spindle neurons which are unique to all those brains that are thought to be responsible for social organization, empathy, speech, and emotion, may also be present even in non-mammalian convergently related groups with equivalent behavior competence.

Materials and Methods

An approximate ten-year-old parrot, remarkably capable of imitating human voice was tamed and caged for behavioral studies for two years. This parrot died naturally and the brain had been dissected out and immediately fixed in 4% Paraformaldehyde in 0.1m phosphate buffer (4°C, pH 7.4) for four days. Two budgerigars (Melopsittacus undulatus) approximately five years old were purchased from local bird market of Allahabad (U. P), India. A combination of Ketamine (24 mg/Kg) and Xylazine (12mg/Kg) was injected through the vein of left leg to anesthetize. Animals initially perfused intracardially with physiological saline (0.9% NaCl) at 4°C and then with fixative solution (2% Paraformaldehyde in 0.1m phosphate buffer 4°C, pH 7.4). Two adult chickens (Gallus gallus) had also been purchased. Their brains were removed quickly and kept in the same fixative solution overnight.

Brains of all the specimens were cut along the sagittal plane and divided into two hemispheres.

Golgi staining

After fixation the left hemispheres of telencephalon of all the specimens were incubated in a chromating solution of 2% potassium dichromate and 5% glutaraldehyde for approximately 3 days (Golgi- Colonnier method). Metal impregnation was then done in 0.75% silver nitrate solution for 24–36 hours. After the first round of staining, the chromation and silver impregnation steps were repeated twice for two days, with gradually increasing the length of the silvering time and reduction of chroming time. In all the cases tissues were washed in distilled water between changes in solutions and fixative was replaced with a freshly prepared solution. Approximately 25 ml of solution was used for each brain and kept in the dark. After the completion of third and final impregnation all the pieces were dehydrated for two to five minutes immersions in increasing concentrations of alcohol, and then in xylene for 5 min. Finally, hemispheres were immediately embedded in paraffin at 37°C and sectioned at 100 μm on a sliding microtome. Sections were then proceeded to remove paraffin by treating with xylene and 100% ethanol. Sections were then mounted on clean slides and cover-slipped using DPX.

Nissl stain

Paraffin blocks of the right hemisphere of all specimens were prepared, 20 μm serial sections were cut by sliding microtome and sections were hydrated through a cold decreasing ethanol series and incubated for approximately 5 minutes in a filtered 0.5% cresyl violet (Sigma) solution prepared in acetate buffer (0.1 M, pH 3.5). The sections were differentiated and dehydrated in 95% and 100% ethanol, cleared in the xylene substitute and cover slipped with DPX.

Sections were studied and photographed by using a digital photo automat camera (Nikon). Single neurons were traced, and drawings of neurons were prepared with a camera Lucida. Serial sections from both hemispheres of the brain were studied for detailed morphological analysis of Golgi-impregnated and Nissl stained neurons.

The vocal control nuclei in parrot, has been identified with the help of budgerigar brain atlas in which, these vocal areas are previously identified by a combination of methods, which includes tract tracing, Nissl staining of brain sections, lesioning of specific brain regions, electrophysiological recordings [45-47] and vocalizing driven gene (ZENK) expression [48-49]. Boundaries of all nine vocal control nuclei, as well as other nuclei, have been identified and traced in each Nissl stained series sections. All the telencephalic, thalamic and mesencephalic nuclei were clearly demarcated due to staining of various degrees. Morphologically distinct neuronal classes present in vocal counterparts have also been studied by Golgi-impregnation method. The neurons which were well impregnated were used to study the detailed morphological analysis. Morphometry and scales shown in Photomicrographs and drawings were determined by ocular scale calibrated for each objective using a stage micrometer.

Statistical analysis

We performed Sholl analysis [50] for Morphometry using ‘simple Neurite tracer’ Image J (Fiji) to characterize the morphologic neuronal class of imaged neuron. The Initial quantification of a neuron is performed by counting the number of dendritic intersections for concentric circles, usually centered at the center of soma, of the gradually increasing Sholl radius. Using Sholl analysis we selected variables that contributed most to the overall variability to distinguish different neuronal types.

Terminology and abbreviations are used according to revised nomenclature for telencephalon and some related brainstem nuclei [51,52].


Parrot brain is the largest sized brain among birds and has a noticeable notch between both large cerebral hemispheres that isolates the telencephalon into two halves. In the dorsal view, telencephalon is narrowed at the rostral side (Figures 1A, B, and C). Indian parrot the- Psittacula krameri are characterized by high EQ values that suggest high brain volumes in relation to their body masses; parrot brains are structured differently than the brains of other vocal learning birds, likesongbirds and hummingbirds. Here detailed anatomical investigation of the brain of Indian parrot–reveal that its neuroarchitecture and brain wiring is unique with specialized cells and without multilayered cortical structure. All the telencephalic, thalamic and mesencephalic areas show the varied staining intensity in Nissl stain and thus are clearly demarcated. Figures 1A-D represents the dorsal, ventral, lateral view of parrot brain. The vertical lines in (Figure 1E) indicate the locations of the sections of interest. The outlines of different nuclear parts of green ring neck Parrot were found to be almost same when compared with budgerigar vocal areas. Outline of each of these areas has been prepared by using camera Lucida (Figures 2A–F). Detailed examination of Nissl and Golgi stained transverse series sections of brain of two species of parrot unveiled the presence of specialized class of neurons in several locations in lateral medial regions of telencephalon, particularly, in Nidopallium Caudolaterale (NCL), dorsolateral corticoid region (CDL), Arcopallium (A) and their corresponding vocal nuclei. All these areas were identified on the basis of the Modern consensus view of the avian brain as described by Jarvis [53] (Figure 2A-F). These regions accomplish sensory processing, motor control and sensory-motor learning in birds similar to the mammalian neocortex. In these brain regions, we discovered the presence of two unique cell morphotype comparable to Von Economo Neurons (VENs) and fork cells in humans, great apes, [23,36,24], and macaque monkey [30]. The neurons which share morphological similarities described by the classical neuroanatomists such as Von Economo [53] in humans, classified as VENs on the basis of the presence of a large elongated soma, a prominent basal and apical dendrite and presence of the nearest complete pyramidal neurons [23] and fork neurons [30]. VENs were identified as large, rod and corkscrew, atypical pyramidal type, bipolar, projection neurons- characterized with elongated, spindle- shaped perikaryon, large apical dendrite, and a single basal dendrite with very sparse branching (Figures 3A and B). Fork cells are characterized by bifurcated long apical dendrites and a single basal dendrite, (Figure 3G) analogous to the fork cells found in frontoinsular, the cortex of humans, great apes [54] and macaque monkey [30]. Both are exceptional neuronal type present intermingled with each other and were larger than neighboring pyramidal cells (Figures 3E-G) and noticeably larger than surrounding fusiform neurons (Figures 3I & 4C, D). Figure 3-A, B illustrate the magnifying view of VENs and (Figure C) demonstrate magnified soma of a VEN. Specific alteration of both these neuronal type in humans is noticed in behavior variant frontotemporal dementia [39,42] and associated with social awareness, empathy, and control of appetite [39]. Lateral part of Oval nucleus of anterior nidopallium (NAOc) and the central Nucleus of the Lateral nidopallium (NLc), (Figures 2A-D) contributes to, the Nidopallium Caudolaterale (NCL) region - a callopallial anterior region of the telencephalon. NCL was located posterior- laterally in nidopallium towards the lateral side of arcopallium (Figures 1B, 2D and 4A). In this nucleus, the cells were arranged in both radial and vertical fashion and can be distinguished as large spindle-shaped bipolar neurons (VENs) Pyramidal neurons (PY), and Fork neurons (F) (Figure 4C). VENs and fork cells are also predominantly confined to another well-demarcated nucleus in parrot telencephalon- the AAC (Figure 4D) - located towards the caudomedial side of NLC (Figures 1E, 2D, 4A, and 4B) covers the rostral part of arcopallium (Figures 2D and 4A). These cells were more dispersed in AAC in comparison to NCL (Figure 4D).