Search PubMed⌕ Search

Biomedical subjects

Peter L Hurd

Publications and source records attributed to Peter L Hurd.

12 recordsLinked to original sources
PubMed2006

Comparative morphology of the avian cerebellum: II. Size of folia.

Despite the highly conserved circuitry of the cerebellum, its overall shape varies significantly among and within vertebrate classes. In birds, one of the most prominent differences among orders is the relative size of the cerebellar folia. The enlargement/reduction of individual folia is thought to relate to specific behavioral differences among taxa, but this has not been adequately tested. Here, we survey variation in cerebellar folia size among 96 species of birds and test for phylogenetic effects and correlations with behavior using a combination of conventional and phylogeny-based statistics. Overall, we found that phylogenetic history accounts for a significant amount of variation in the relative size of individual folia. Order membership, in particular, accounted for more than half of the interspecific variation in folia size. There are also complex relationships among folia such that the expansion of one folium is often accompanied by a reduction in other folia. With respect to behavioral correlates: (1) we did not find any significant correlations between folia size and reliance on trigeminal input; (2) there was some evidence supporting a correlation between strong hindlimbs and an expansion of the anterior lobe; and (3) there were significant reductions in folia I-III and expansions in folia VI and VII in species classified as strong fliers. This expansion likely reflects increased visual processing requirements in species with rapid and/or agile flight. It therefore appears that folium size is a product of both phylogenetic history and behavior in birds.

Animals↗
PubMed2006

Comparative morphology of the avian cerebellum: I. Degree of foliation.

Despite the conservative circuitry of the cerebellum, there is considerable variation in the shape of the cerebellum among vertebrates. One aspect of cerebellar morphology that is of particular interest is the degree of folding, or foliation, of the cerebellum and its functional significance. Here, we present the first comprehensive analysis of variation in cerebellar foliation in birds with the aim of determining the effects that allometry, phylogeny and development have on species differences in the degree of cerebellar foliation. Using both conventional and phylogenetically based statistics, we assess the effects of these variables on cerebellar foliation among 91 species of birds. Overall, our results indicate that allometry exerts the strongest effect and accounts for more than half of the interspecific variation in cerebellar foliation. In addition, we detected a significant phylogenetic effect. A comparison among orders revealed that several groups, corvids, parrots and seabirds, have significantly more foliated cerebella than other groups, after accounting for allometric effects. Lastly, developmental mode was weakly correlated with relative cerebellar foliation, but incubation period and fledging age were not. From our analyses, we conclude that allometric and phylogenetic effects exert the strongest effects and developmental mode a weak effect on avian cerebellar foliation. The phylogenetic distribution of highly foliated cerebella also suggests that cognitive and/or behavioral differences play a role in the evolution of the cerebellum.

Analysis of Variance↗
PubMed2006

Resource holding potential, subjective resource value, and game theoretical models of aggressiveness signalling.

Empirical evidence suggests that aggressiveness (willingness to enter into, or escalate an aggressive interaction) may be more important than the ability to win fights in some species. Both empirical and theoretical traditions treat aggressiveness as a distinct property from the ability (RHP) or motivation (subjective resource value) to win a fight. I examine how these three traits are clearly distinct when modelled using a simple strategic model of escalation. I then examine game theoretical models of agonistic communication and demonstrate that models in which aggressiveness is signalled require: (1) a trait, aggressiveness, which is neither a correlate, nor consequence of RHP or motivation, (2) a handicap which negates any benefit to be gained through the use of a particular signal, and (3) the absence of any other asymmetry which could be used to assign roles to players. I conclude that it is unlikely that these assumptions are ever met, and that empirical examples of "aggressiveness" are far more likely to represent long-term differences in subjective resource value.

Aggression↗
PubMed2005

The comparative morphology of the cerebellum in caprimulgiform birds: evolutionary and functional implications.

Interspecific variation in the structure of the avian cerebellum is poorly understood. We present the first comparison of cerebellar morphology within the avian order Caprimulgiformes. Using a range of qualitative descriptions and quantitative measurements of cerebellar morphology we compared caprimulgiform birds with hummingbirds and swifts (Apodiformes) and owls (Strigiformes), two groups that are putative sister taxa to the Caprimulgiformes. Our results demonstrate that the owlet-nightjars (Aegothelidae), nightjars (Caprimulgidae) and potoos (Nyctibiidae) are more similar to apodiforms than they are to other taxa. All of these species have a reduced anterior lobe characterized by particularly small folia II and III and a relatively large posterior lobe. The frogmouths (Podargidae) possess a markedly different cerebellum that is more similar to that of owls than any of the caprimulgiform or apodiform birds. The monotypic oilbird (Steatornis caripensis, Steatornithidae) possesses a cerebellum with some nightjar-like features and some owl-like features, but overall it too resembles an owl more than a nightjar. This cerebellar diversity within the order Caprimulgiformes has significant implications for understanding the evolutionary relationships within the order, how the avian cerebellum has evolved and whether interspecific differences in cerebellar morphology reflect behavior.

Animals↗
PubMed2005

Inferior olivary neurons innervate multiple zones of the flocculus in pigeons (Columba livia).

Complex spike activity of floccular Purkinje cells responds to patterns of rotational optic flow about the vertical axis (rVA neurons) or a horizontal axis 45 degrees to the midline (rH45 neurons). The pigeon flocculus is organized into four parasagittal zones: two rVA zones (zones 0 and 2) interdigitated with two rH45 zones (zones 1 and 3). Climbing fiber input to the rVA and rH45 zones arises in the caudal and rostral regions of the medial column of the inferior olive (mcIO), respectively. To determine whether the two rVA zones and the two rH45 zones receive input from different areas of the caudal and rostral mcIO and whether individual neurons project to both zones of the same rotational preference, different colors of fluorescent retrograde tracer were injected into the two rVA or two rH45 zones. For the rVA injections, retrogradely labeled cells from the two zones were intermingled in the caudal mcIO, but the distribution of cells labeled from zone 0 was slightly caudal to that from zone 2. On average, 18% of neurons were double labeled. For the rH45 injections, cells retrogradely labeled from the two zones were intermingled in the rostral mcIO, but the distribution of cells labeled from zone 1 was slightly rostral to that from zone 3. On average, 22% of neurons were double labeled. In sum, each of the two rVA zones and the two rH45 zones receives input from slightly different regions of the mcIO, and about 20% of the neurons project to both zones.

Animals↗
PubMed2005

The evolution of cerebrotypes in birds.

Multivariate analyses of brain composition in mammals, amphibians and fish have revealed the evolution of 'cerebrotypes' that reflect specific niches and/or clades. Here, we present the first demonstration of similar cerebrotypes in birds. Using principal component analysis and hierarchical clustering methods to analyze a data set of 67 species, we demonstrate that five main cerebrotypes can be recognized. One type is dominated by galliforms and pigeons, among other species, that all share relatively large brainstems, but can be further differentiated by the proportional size of the cerebellum and telencephalic regions. The second cerebrotype contains a range of species that all share relatively large cerebellar and small nidopallial volumes. A third type is composed of two species, the tawny frogmouth (Podargus strigoides) and an owl, both of which share extremely large Wulst volumes. Parrots and passerines, the principal members of the fourth group, possess much larger nidopallial, mesopallial and striatopallidal proportions than the other groups. The fifth cerebrotype contains species such as raptors and waterfowl that are not found at the extremes for any of the brain regions and could therefore be classified as 'generalist' brains. Overall, the clustering of species does not directly reflect the phylogenetic relationships among species, but there is a tendency for species within an order to clump together. There may also be a weak relationship between cerebrotype and developmental differences, but two of the main clusters contained species with both altricial and precocial developmental patterns. As a whole, the groupings do agree with behavioral and ecological similarities among species. Most notably, species that share similarities in locomotor behavior, mode of prey capture or cognitive ability are clustered together. The relationship between cerebrotype and behavior/ecology in birds suggests that future comparative studies of brain-behavior relationships will benefit from adopting a multivariate approach.

Animals↗
PubMed2005

Finger length ratio (2D:4D) correlates with physical aggression in men but not in women.

Finger length ratio (2D:4D) is a sexually dimorphic trait. Men have relatively shorter second digits (index fingers) than fourth digits (ring fingers). Smaller, more masculine, digit ratios are thought to be associated with either higher prenatal testosterone levels or greater sensitivity to androgens, or both. Men with more masculine finger ratios are perceived as being more masculine and dominant by female observers, and tend to perform better in a number of physical sports. We hypothesized that digit ratio would correlate with propensity to engage in aggressive behavior. We examined the relationship between trait aggression, assayed using a questionnaire, and finger length ratio in both men and women. Men with lower, more masculine, finger length ratios had higher trait physical aggression scores (r(partial) = -0.21, N = 134, P = 0.028). We found no correlation between finger length ratio and any form of aggression in females. These results are consistent with the hypothesis that testosterone has an organizational effect on adult physical aggression in men.

Adolescent↗
PubMed2004

Spatiotemporal tuning of optic flow inputs to the vestibulocerebellum in pigeons: differences between mossy and climbing fiber pathways.

The pretectum, accessory optic system (AOS), and vestibulocerebellum (VbC) have been implicated in the analysis of optic flow and generation of the optokinetic response. Recently, using drifting sine-wave gratings as stimuli, it has been shown that pretectal and AOS neurons exhibit spatiotemporal tuning. In this respect, there are two groups: fast neurons, which prefer low spatial frequency (SF) and high temporal frequency (TF) gratings, and slow neurons, which prefer high SF-low TF gratings. In pigeons, there are two pathways from the pretectum and AOS to the VbC: a climbing fiber (CF) pathway to Purkinje cells (P cells) via the inferior olive and a direct mossy fiber (MF) pathway to the granular layer (GL). In the present study, we assessed spatiotemporal tuning in the VbC of ketamine-anesthetized pigeons using standard extracellular techniques. Recordings were made from 17 optic-flow-sensitive units in the GL, presumably granule cells or MF rosettes, and the complex spike activity (CSA) of 39 P-cells, which reflects CF input. Based on spatiotemporal tuning to gratings moving in the preferred direction, eight GL units were classified as fast units, with a primary response to low SF-high TF gratings (mean = 0.13 cpd/8.24 Hz), whereas nine were slow units preferring high SF-low TF gratings (mean = 0.68 cpd/0.30 Hz). CSA was almost exclusively tuned to slow gratings (mean = 0.67 cpd/0.35 Hz). We conclude that MF input to the VbC is from both fast and slow cells in the AOS and pretectum, whereas the CF input is primarily tuned to slow gratings.

Action Potentials↗
PubMed2004

A dissociation of motion and spatial-pattern vision in the avian telencephalon: implications for the evolution of "visual streams".

The ectostriatum is a large visual structure in the avian telencephalon. Part of the tectofugal pathway, the ectostriatum receives a large ascending thalamic input from the nucleus rotundus, the homolog of the mammalian pulvinar complex. We investigated the effects of bilateral lesions of the ectostriatum in pigeons on visual motion and spatial-pattern perception tasks. To test motion perception, we measured performance on a task requiring detection of coherently moving random dots embedded in dynamic noise. To test spatial-pattern perception, we measured performance on the detection of a square wave grating embedded in static noise. A double dissociation was revealed. Pigeons with lesions to the caudal ectostriatum showed a performance deficit on the motion task but not the grating task. In contrast, pigeons with lesions to the rostral ectostriatum showed a performance deficit on the grating task but not the motion task. Thus, in the avian telencephalon, there is a separation of visual motion and spatial-pattern perception as there is in the mammalian telencephalon. However, this separation of function is in the targets of the tectofugal pathway in pigeons rather than in the thalamofugal pathway as described in mammals. The implications of these findings with respect to the evolution of the visual system are discussed. Specifically, we suggest that the principle of parallel visual streams originated in the tectofugal pathway rather than the thalamofugal pathway.

Analysis of Variance↗
PubMed2003

Generalization in response to mate recognition signals.

Females usually exhibit strong and unequivocal recognition of conspecific mating signals and reject those of other sympatric heterospecifics. However, most species are allopatric with one another, and the degree to which females recognize mating signals of allopatric species is more varied. Such mating signals are often rejected but are sometimes falsely recognized as conspecific. We studied the dynamics of mate recognition in female túngara frogs (Physalaemus pustulosus) in response to a series of calls that were intermediate between the conspecific and each of five allopatric-heterospecific calls: two that elicited recognition from females in previous studies and three that did not. This study shows that females perceive variation in allopatric mating signals in acontinuous manner with no evidence of perceptual category formation. The strength of recognition is predicted by how different the target stimulus is from the conspecific call within a series of calls. But the differences in recognition responses among call series are not predicted by the similarity of the call series to the conspecific call. The latter result suggests that the strength of recognition of allopatric signals might be influenced by processes of stimulus generalization and past evolutionary history.

Acoustic Stimulation↗
PubMed1998

Discrete conventional signalling of a continuous variable.

In aggressive interactions, animals often use a discrete set of signals, while the properties being signalled are likely to be continuous, for example fighting ability or value of victory. Here we investigate a particular model of fighting that allows for conventional signalling of subjective resource value to occur. Perfect signalling and no signalling are not evolutionarily stable strategies (ESSs) in the model. Instead, we find ESSs in which partial information is communicated, with discrete displays signalling a range of values rather than a precise one. The result also indicates that communication should be more precise in conflicts over small resources. Signalling strategies can exist in fighting because of the common interest in avoiding injuries, but communication is likely to be limited because of the fundamental conflict over the resource. Our results reflect a compromise between these two factors. Data allowing for a thorough test of the model are lacking; however, existing data seem consistent with the obtained theoretical results. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗