Whisking in animals

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Rats using their mystacial vibrissae to perform whisking Rat noses.jpg
Rats using their mystacial vibrissae to perform whisking

Whisking is a behaviour in which the facial whiskers (vibrissae) of an animal are repetitively and rapidly swept back and forth. This behaviour occurs particularly during locomotion and exploration. The whisking movements occur in bouts of variable duration, and at rates between 3 and 25 whisks/second. Movements of the whiskers are closely co-ordinated with those of the head and body, allowing the animal to locate interesting stimuli through whisker contact, then investigate them further using both the macrovibrissae and an array of shorter, non-actuated microvibrissae on the chin and lips. Whisking has been reported in a wide range of mammals, including two species of marsupial. Whisking contributes both to exploratory movements, which function to acquire sensory inputs, and to palpation movements, which are used in the discrimination of objects and in the control of spatial navigation. [1]

Contents

Types

There are three types of whisking. Exploratory whisking occurs when animals whisk in air without contact or with only light contact. In this case, the stroke on a given whisk approaches 70°, and a total field of up to 160° may be covered as the animal slowly shifts the set point of its whisk. Such whisking is extremely regular and typically occurs with a frequency between 7 and 12 Hz and a mean of 9 Hz. Asymmetric whisking occurs when animals make contact with a large object, such as a wall, while they whisk. It also occurs if they turn their head to the side while whisking. Asymmetric whisking lasts for only one to three whisk cycles. Foveal whisking occurs when animals thrust all their vibrissae forward to palpate an object ahead of them, as occurs when they try to detect a landing on the far side of a gap. In this case the stroke is much reduced, typically to 20°. The frequency of foveal whisking is high, ranging between 15 and 25 Hz, and rats can readily switch between foveal and exploratory whisking. [2]

Facial vibrissae

Many land and marine mammals possess facial vibrissae (derived from the Latin "vibrio" meaning to vibrate). For example, rats [3] and hamsters, [4] have an arrangement of cranial (of the skull) vibrissae that includes the supraorbital (above the eyes), genal (of the cheeks), and mystacial (where a moustache would be) vibrissae, as well as mandibular (of the jaw) vibrissae under the snout. [5] Mystacial vibrissae are generally described as being further divided into two sub-groups: the large macrovibrissae that protrude to the sides, and the small microvibrissae below the nostrils that mostly point downwards. [6] The macrovibrissae are generally large, motile and used for spatial sensing, whereas microvibrissae are small, immotile and used for object identification.

Musculature and nervous system

Generally, the supraorbital, genal and macrovibrissae are reported to be motile, [4] whilst the microvibrissae are not. This is reflected in anatomical reports that have identified musculature associated with the macrovibrissae that is absent for the microvibrissae. [7]

The effector system generating whisking comprises a set of “extrinsic” muscles controlling movements of the mystacial pad and a group of “intrinsic” (follicular) muscles, producing vibrissa protraction. The extrinsic muscles in the mystacial pad move many or all of the macrovibrissae together. [7] [8] However, the individual follicles of some groups of facial vibrissae in some species are also motile. A small muscle 'sling' is attached to each macrovibrissa and can move it more-or-less independently of the others. Vibrissa retraction is thought to be a passive process produced by rebound of stretched follicular muscle. Whisking movements are amongst the fastest produced by mammals[ citation needed ]. In animals that are capable of whisking at high frequencies, the whisking musculature contains a high proportion of type 2B muscle fibers that can support faster contractions than normal skeletal muscles. [9]

Sensory innervation of the whiskers is provided by the infraorbital branch of the trigeminal maxillary nerve; motor innervation is attributable to the facial (VII) nerve. [1]

Species that whisk

Amongst those species with motile macrovibrissae, some (rats, mice, flying squirrels, gerbils, chinchillas, hamsters, shrews, porcupines, opossums) [10] perform whisking. [11] Although whisking is prominent in rodents, there are several rodent genera, such as capybara and gophers, that do not appear to whisk, and others, such as guinea pigs, that display only irregular and relatively short whisking bouts [9] Whisking behaviour has not been observed in carnivores (e.g. cats, dogs, raccoons, bears), [10] although some species, such as pinnipeds, have well-developed sinus muscles making the whiskers highly motile. [12]

Control and co-ordination

In rats, whisking movements occur in bouts of variable duration at rates between 3 and 25 whisks/second. [10] The movements have an amplitude over a range from ∼10 to 100°, at an average protraction velocity of ∼1000°/sec, and at a predominant frequency of 5–7 Hz. [1] Three types of whisk are described, single, delayed (there is an inflection point somewhere in the whisk's velocity) or double-pumped (slight retraction in the middle of the whisk followed by protraction to complete the whisk cycle). [13]

Whisking movements relative to the head are described by 3 angles of rotation (azimuth, ; elevation, ; and torsion, ) and translations of the whisker base. Azimuthal rotation moves the whiskers back and forth along the longitudinal axis. This movement co-varies with small changes in elevation. Torsion (or, roll) refers to a rotation of a whisker about its own axis. The torsional angle is correlated with the azimuth, and alters the forward facing surface of the whisker shaft that contacts the opposing surface. Because the vibrissae are curved, torsion also displaces the whisker tips relative to the head. [14] [15]

Early studies (1964) described co-ordination between vibrissae, nose, head, and sniffing movements. From these studies it was suggested that the animal's whisking behaviour is dependent on the task and that whisking during exploratory behaviors is different from whisking during discriminative behaviours. [13]

In all whisking animals in which it has so far been measured, these whisking movements are rapidly controlled in response to behavioural and environmental conditions. Movements of the whiskers are closely co-ordinated with those of the head and body. [10]

Sniffing, a high-frequency, highly rhythmic inhalation and exhalation of air through the nose, plays an important role in rodent olfaction. Whisking is thought to be co-ordinated with sniffing and normal respiratory behaviour. It has been shown that breathing and whisking movements are correlated only when the whisking rhythm is less than 5 Hz. Only 13% of whisking movements occur during high-frequency (greater than 5 Hz) respiration typically associated with sniffing, indicating that high-frequency whisking and sniffing behaviours are not correlated. [16]

Whisking and sniffing also constitute the overt expression of an animal's anticipation of a reward. [17]

Development

In rats, whiskers grow to their adult size in the first month of life, although, rats sustaining denervation of the whisker pad grow whiskers that are thinner and smaller than those of normal adults. Whisking begins around post-natal day 11 to 13, prior to the eyes opening, and achieves adult amplitudes and characteristics by the end of the third post-natal week. Prior to the onset of whisking, neonatal rats show behavioural activation in response to whisker stimulation, and tactile learning in a classical conditioning avoidance paradigm, but are not able to orient to the stimulus source. Micro-movements of the vibrissae in the first ten days of life have also been observed. [10]

Related Research Articles

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A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. In contrast, in smooth pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements.

Whiskers type of mammalian hair used for sensing

Whiskers or vibrissae are a type of mammalian hair that are typically characterised, anatomically, by their long length, large and well-innervated hair follicle, and by having an identifiable representation in the somatosensory cortex of the brain.

Claustrum structure in the brain, gray matter lamina located underneath the inner neocortex

The claustrum is a thin, bilateral structure that connects to cortical and subcortical regions of the brain. It is located between the insula laterally and the putamen medially, separated by the extreme and external capsules respectively. The blood supply to the claustrum is fulfilled via the middle cerebral artery. It is considered to be the most densely connected structure in the brain, allowing for integration of various cortical inputs into one experience rather than singular events. The claustrum is difficult to study given the limited number of individuals with claustral lesions and the poor resolution of neuroimaging.

Motor cortex Region of the cerebral cortex

The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements. Classically, the motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.

In physiology, tonotopy is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain. Tonotopic maps are a particular case of topographic organization, similar to retinotopy in the visual system.

Barrel cortex

The barrel cortex is a region of the somatosensory cortex that is identifiable in some species of rodents and species of at least two other orders and contains the barrel field. The 'barrels' of the barrel field are regions within cortical layer IV that are visibly darker when stained to reveal the presence of cytochrome c oxidase and are separated from each other by lighter areas called septa. These dark-staining regions are a major target for somatosensory inputs from the thalamus, and each barrel corresponds to a region of the body. Due to this distinctive cellular structure, organisation, and functional significance, the barrel cortex is a useful tool to understand cortical processing and has played an important role in neuroscience. The majority of what is known about corticothalamic processing comes from studying the barrel cortex, and researchers have intensively studied the barrel cortex as a model of neocortical column.

Stria terminalis Band of fibres along the thalamus

The stria terminalis is a structure in the brain consisting of a band of fibers running along the lateral margin of the ventricular surface of the thalamus. Serving as a major output pathway of the amygdala, the stria terminalis runs from its centromedial division to the ventromedial nucleus of the hypothalamus.

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Frontal eye fields

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Hydrodynamic reception

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Ultrasonic vocalization

Ultrasonic vocalizations (USVs) occur at frequencies ranging from approximately 20–100 kHz. They are emitted by animals such as bats and rodents, and have been extensively studied in rats and mice. As opposed to sonic vocalizations, ultrasonic vocalizations cannot be detected by the human ear. USVs serve as social signals, and are categorized according to their frequency. Different categories of USVs are elicited in response to different situations and varying affective states. The behavioural functions of USVs vary as a rat or mouse pup reaches the juvenile/adult stage of their development. The brain mechanisms behind calling behaviour have also been studied, and some studies have used pharmacological manipulation.

References

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  2. ↑ Kleinfeld, D. (2008). "Vibrissa movement, sensation and sensorimotor control" (PDF). Retrieved September 30, 2013.
  3. ↑ Vincent, SB (1913). "The tactile hair of the white rat". The Journal of Comparative Neurology. 23 (1): 1–34. doi:10.1002/cne.900230101.
  4. 1 2 Wineski, L.E. (1983). "Movements of the cranial vibrissae in the Golden hamster (Mesocricetus auratus)". Journal of Zoology. 200 (2): 261–280. doi:10.1111/j.1469-7998.1983.tb05788.x.
  5. ↑ Thé, L; Wallace, ML; Chen, CH; Chorev, E; Brecht, M (2013). "Structure, function, and cortical representation of the rat submandibular whisker trident". The Journal of Neuroscience. 33 (11): 4815–4824. doi:10.1523/jneurosci.4770-12.2013. PMC   6619006 . PMID   23486952.
  6. ↑ Brecht, M.; Preilowski, B.; Merzenich, M.M. (1997). "Functional architecture of the mystacial vibrissae". Behavioural Brain Research. 84 (1–2): 81–97. doi:10.1016/S0166-4328(97)83328-1. PMID   9079775. S2CID   3993159.
  7. 1 2 Dorfl, J (1982). "The musculature of the mystacial vibrissae of the white mouse". Journal of Anatomy. 135 (Pt 1): 147–54. PMC   1168137 . PMID   7130049.
  8. ↑ Hill, D.N.; Bermejo, R.; Zeigler, H.P.; Kleinfeld, D. (2008). "Biomechanics of the vibrissa motor plant in rat: Rhythmic whisking consists of triphasic neuromuscular activity". The Journal of Neuroscience. 28 (13): 3438–3455. doi: 10.1523/JNEUROSCI.5008-07.2008 . PMC   6670594 . PMID   18367610.
  9. 1 2 Jin, T-E; Witzemann, V; Brecht, M (2004). "Fiber types of the intrinsic whisker muscle and whisking behavior". The Journal of Neuroscience. 24 (13): 3386–3393. doi: 10.1523/JNEUROSCI.5151-03.2004 . PMC   6730039 . PMID   15056718.
  10. 1 2 3 4 5 Prescott, TJ; Mitchinson, B; Grant, RA (2011). "Vibrissal behaviour and function". Scholarpedia. 6 (10): 6642. Bibcode:2011SchpJ...6.6642P. doi: 10.4249/scholarpedia.6642 . Retrieved September 30, 2013.
  11. ↑ "Video of rat whisking". Youtube.com. Retrieved 2013-06-24.
  12. ↑ Ahl, AS (1986). "The role of vibrissae in behavior - a status review". Veterinary Research Communications. 10 (4): 245–268. doi:10.1007/bf02213989. PMID   3526705. S2CID   8243656.
  13. 1 2 Moxon, K.A. (2008). "Natural Whisking. Focus on "Variability in Velocity Profiles During Free-Air Whisking Behavior of Unrestrained Rats"" . Retrieved October 2, 2013.
  14. ↑ Knutsen, PM; Biess, A; Ahissar, E (2008). "Vibrissal Kinematics in 3D: Tight Coupling of Azimuth, Elevation, and Torsion across Different Whisking Modes". Neuron. 59 (1): 35–42. doi: 10.1016/j.neuron.2008.05.013 . PMID   18614027.
  15. ↑ Knutsen, PM (2015). "Whisking Kinematics". Scholarpedia. 10 (3): 7280. doi: 10.4249/scholarpedia.7280 .
  16. ↑ Cao, Y; Roy, S; Sachdev, RN; Heck, DH (2012). "Dynamic correlation between whisking and breathing rhythms in mice". Journal of Neuroscience. 32 (5): 1653–9. doi:10.1523/JNEUROSCI.4395-11.2012. PMC   3567452 . PMID   22302807.
  17. ↑ Deschênes, M; Moore, J; Kleinfeld, D (2012). "Sniffing and whisking in rodents". Current Opinion in Neurobiology. 22 (2): 243–250. doi:10.1016/j.conb.2011.11.013. PMC   4934665 . PMID   22177596.
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