Evoked responses in the chicken telencephalon to auditory, visual, and tactile stimulation

The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago

Vertebrates evolved in the Cambrian Period before 520 million years ago, but we do not know when or how consciousness arose in the history of the vertebrate brain. Here we propose multiple levels of isomorphic or somatotopic neural representations as an objective marker for sensory consciousness. All extant vertebrates have these, so we deduce that consciousness extends back to the group's origin. The first conscious sense may have been vision. Then vision, coupled with additional sensory systems derived from ectodermal placodes and neural crest, transformed primitive reflexive systems into image forming brains that map and perceive the external world and the body's interior. We posit that the minimum requirement for sensory consciousness and qualia is a brain including a forebrain (but not necessarily a developed cerebral cortex/pallium), midbrain, and hindbrain. This brain must also have (1) hierarchical systems of intercommunicating, isomorphically organized, processing nuclei that extensively integrate the different senses into representations that emerge in upper levels of the neural hierarchy; and (2) a widespread reticular formation that integrates the sensory inputs and contributes to attention, awareness, and neural synchronization. We propose a two-step evolutionary history, in which the optic tectum was the original center of multi-sensory conscious perception (as in fish and amphibians: step 1), followed by a gradual shift of this center to the dorsal pallium or its cerebral cortex (in mammals, reptiles, birds: step 2). We address objections to the hypothesis and call for more studies of fish and amphibians. In our view, the lamprey has all the neural requisites and is likely the simplest extant vertebrate with sensory consciousness and qualia. Genes that pattern the proposed elements of consciousness (isomorphism, neural crest, placodes) have been identified in all vertebrates. Thus, consciousness is in the genes, some of which are already known.

Rostral wulst of passerine birds: II. Intratelencephalic projections to nuclei associated with the auditory and song systems

We have previously shown that the hyperstriatum accessorium (HA) of the rostral wulst in zebra finches and green finches is the origin of a pyramidal-like tract with substantial projections to the brainstem and cervical spinal cord. Here, we show that the HA also is the origin of a set of intratelencephalic projections with terminal fields in the lateral part of the frontal neostriatum, the shell surrounding the lateral magnocellular nucleus of the anterior neostriatum, the lobus parolfactorius surrounding area X, the nucleus interface, auditory fields L1 and L3, the shelf underlying the high vocal center, the dorsolateral caudal neostriatum, the dorsocaudal part of the nucleus robustus archistriatalis, and the ventral archistriatum. The cells of origin of these projections are located predominantly laterally in the HA, close to and sometimes within the intercalated HA, which receives somatosensory projections from the dorsal thalamus. The specific implications of these findings for auditory and vocal function are unclear, but the apparent overlap of auditory and somatosensory inputs in several of these regions suggests the possibility of mechanisms for stimulus enhancement or depression, depending on the congruence of stimuli within a cell's "in-register" multiple receptive fields.

Intratelencephalic projections of the visual wulst in pigeons (Columba livia)

The visual wulst is the telencephalic target of the thalamofugal visual pathway of birds, and thus the avian equivalent of the striate cortex of mammals. The anterograde tracer Phaseolus vulgaris leucoagglutinin was used to follow the intratelencephalic connections of the major constituents of the visual wulst in pigeons. In particular, efferent pathways from the granular layer (Intercalated nucleus of the hyperstriatum accessorium, IHA), supragranular layer (hyperstriatum accessorium, HA), and infragranular layers (hyperstriatum intercalatus superior and/or hyperstriatum dorsale, HIS/HD) were investigated. These efferent projections were confirmed by injections of the retrograde tracer cholera toxin subunit B into their terminal fields. When a deposit of the anterograde tracer was centered in IHA, which receives the visual thalamic input, efferent fibers were seen mainly dorsomedially to IHA. When a deposit of the anterograde tracer was centered in HA, efferent fibers were seen to extend mainly in three directions: 1) medially to the tractus septomesencephalicus, which sends projections to extratelencephalic visual nuclei: 2) ventrolaterally to the lateral portion of the neostriatum frontale, where there were also labeled cells after the retrograde tracer was injected in HA; and 3) ventromedially to the paleostriatal complex, which is the avian equivalent of the mammalian caudale, 5) neostriatum intermedium, 6) archistriatum intermedium, and 7) hyperstriatum laterale. Finally, HIS/HD have projections predominantly to HA and the dorsocaudal telencephalon (area corticoidea dorsolateralis and area parahippocampalis), as well as relatively minor projections to the areas which also receive projections from HA. No anterogradely labeled fibers were seen in the tractus septomesencephalicus following the tracer injections in HIS/HD. These results indicate that the visual information from the granular layer is distributed via the supragranular layer HA to multiple areas within the telencephalon, such as the neostriatum frontale and paleostriatal complex. In addition, HA is the source of an extratelencephalic projection via the tractus septomesencephalicus. Thus, the avian supragranular layer HA contains neurons which are the source of both intratelencephalic and extratelencephalic projections, whereas neurons of the mammalian cortex are segregated into two distinct layers, supragranular and infragranular layers, based on the targets of their projections. The findings are further discussed and compared to the mammalian striate cortex.

Connections of the auditory forebrain in the pigeon (Columba livia)

Ascending auditory efferents in birds terminate mainly within Field L2, a cytoarchitectonically distinct region of the caudomedial telencephalon. The organization of Field L2, and that of its flanking regions, L1 and L3, was investigated with 14C-2-deoxyglucose (14C-2-DG), cytochrome oxidase, and both retrograde and anterograde tracing techniques. Field L2 was found to contain a high concentration of cytochrome oxidase. Following auditory stimulation, 14C-2-DG autoradiography revealed that Field L2 consists of two adjacent but seemingly discontinuous zones, designated Field L2a, which lies ventromedially, and Field L2b, which lies dorsolaterally. Termination of thalamic efferents: The thalamic auditory nuclei ovoidalis (Ov) and semilunaris parovoidalis (SPO) project predominantly upon Field L2, and possibly sparsely upon L1, L3 and the overlying hyperstriatum ventrale (HV). Ov subnuclei project upon L2a and SPO projects predominantly upon L2b. The topography of the projections is inverted along the ventromedial-to-dorsolateral axis of L2, and is in accord with an inverted tonotopic representation of frequencies; high frequencies (< 3.5 kHz) being found in the more ventromedial parts of L2a, and low frequencies and broad band responses in L2b. Intra- and extratelencephalic connections: Field L2a also receives a substantial projection from HV, but the efferent projections of L2a appear confined to adjacent "neostriatal" regions. The subsequent projections of L2b were not identified in this study. L1 and L3 project predominantly to the dorsal neostriatum (Nd) caudolateral to Field L, and have fewer projections to the caudomedial paleostriatum and anterior hyperstriatum accessorium. Nd projects massively upon the ventromedial nucleus of the intermediate archistriatum (Aivm), which has bilateral projections upon the caudomedial telencephalon and is the origin of a major descending pathway having dense terminations surrounding the ovoidalis complex (Ov and SPO), MLd, the lateral lemniscal nuclei, and sparse terminations within SPO itself. It is suggested that within the telencephalon the major components of the auditory pathway consist of cell groups which collectively correspond to the populations of neurons found within the auditory cortex of mammals.

Somatosensory areas in the telencephalon of the pigeon. II. Spinal pathways and afferent connections

There are two somatosensory areas in the telencephalon of the pigeon which receive an input from the spinal somatosensory system: one in the rostral Wulst which consists of the three hyperstriatal layers (h. accessorium (HA), h. intercalatus superior (HIS) and h. dorsale (HD] and one in the caudal telencephalon (neostriatum caudale (NC), neostriatum intermedium (NI) and hyperstriatum ventrale (HV]. Recordings of evoked single unit or multi unit activity and of field potentials before and after lesions of spinal pathways at a high cervical level (C4) were made to determine the contribution of these pathways to the transmission of somatosensory signals to these telencephalic areas. The rostral Wulst area receives somatic signals only through dorsal tracts contralateral to the recording site. Inputs from the wing arise mainly through the dorsal columns (DC) and those from the leg largely through the dorsolateral funiculus (DLF). The spinal projection pathway to the caudal neostriatal area includes the dorsal tracts and parts of the lateral funiculi on both sides. There was no difference in response form between the wing and leg responses. Signals transmitted through the lateral pathways were found to elicit the earliest responses (6-13 ms, electrical stimulation) in the caudal forebrain, while signals travelling through the DC arrive later in the caudal area (about 14 ms for wing stimulation) than in the rostral Wulst area (about 9 ms). The afferent thalamic and intratelencephalic connections of the two somatosensory areas in the telencephalon of the pigeon were investigated with retrograde transport of the neuronal tracers horseradish-peroxidase (HRP) or wheatgerm agglutinated HRP (WGA-HRP), Fast Blue (FB) and Rhodamine-isothiocyanat (RITC). Small tracer-injections were made under electrophysiological control at somatosensory responsive locations. These investigations confirm the projection of the caudal part of the nucleus dorsolateralis posterior (DLPc) to the caudal area and of the nucleus dorsalis intermedius ventralis anterior (DIVA) to the rostral area. In addition, it could be shown that the NI/NC projects to the HV thus confirming the electrophysiological results reported in a companion paper (Funke 1989) that the HV is a secondary area. The integrative function of HV is supported by connections to other sensory and motor telencephalic areas. Combined injections of FB and RITC revealed a topographic projection from the DIVA to the anterior Wulst.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatosensory areas in the telencephalon of the pigeon. I. Response characteristics

Two somatosensory regions in the pigeon's telencephalon were investigated electrophysiologically with recordings of field potentials as well as single- and multi-unit responses which were evoked by electrical stimulation of all four extremities or by feather movements produced with airpuffs or by hand. The outline of both areas, was studied in detail with the use of grid-like recordings of single or multi-units. One somatosensory area is located rostrally in the hyperstriatum accessorium (HA), rostral to the visual "Wulst". A caudal area comprises the medial aspects of two different cell layers: the neostriatum intermedium (NI) and adjacent neostriatum caudale (NC) as well as the overlying hyperstriatum ventrale (HV). The two areas differ considerably in their response characteristics. Field potentials of the NI/NC-HV area were more complex than those of the HA area and their shapes and latencies varied mainly in dependence of the recording site (NI, NC, HV). Multi-unit responses showed strong excitation and short latencies in NI/NC and weak excitation and longer latencies in HV. Both responses and latencies were uniform in the HA area and latencies generally longer than in NI/NC but shorter than in HV. The HA area processes somatosensory information more specifically. Its neurons have relatively small receptive fields which seem to be arranged in a somatotopic order in such a way that rostral parts of the body are represented superficially and caudal parts in deeper layers. In contrast, the NI/NC-HV area was found to be largely multimodal, receiving also auditory and visual information. Neurons in this region have large somatic receptive fields, often including one and sometimes even both sides of the body surface. A somatotopic arrangement could not be recognized. The whole body surface was representated in both areas, but there was a dominance of wing and back receptive fields in the NI/NC-HV area and leg and neck receptive fields in the HA area.

The avian somatosensory system: connections of regions of body representation in the forebrain of the pigeon

In order to establish the basic connectivity of physiologically identified somatosensory regions of the thalamus and telencephalon in the pigeon, injections of wheatgerm agglutinin-horseradish peroxidase were made under electrophysiological control and the projections were charted following conventional neurohistochemistry. The physiological recordings generally confirmed the findings of Delius and Bennetto (Brain Research, 37 (1972) 205-221) of somatosensory sites within the dorsal thalamus, anterior hyperstriatum and caudomedial neostriatum, and the anatomical results show that the thalamic cells of origin of the projections to the two telencephalic regions are largely separate: a rostral cell group comprising nucleus dorsalis intermedius ventralis anterior projects to the anterior hyperstriatum accessorium (HA), whilst a caudal cell group comprising caudal regions of nucleus dorsolateralis posterior (DLP) projects to the medial neostriatum intermedium and caudale (NI/NC). Caudal DLP is also the origin of a visual projection to NI/NC, and its terminal field also approximates that of the thalamic auditory nucleus ovoidalis. Since the anterior HA and NI/NC were here shown to be reciprocally connected, there is a possibility of multimodal input to both telencephalic regions. HA was also further defined as the origin of the basal branch of the septomesencephalic tract, and hence potentially provides an outlet for both telencephalic somatosensory regions. The results are discussed within a comparative context.

Auditory responses in the nucleus basalis of the pigeon

Single-unit responses and field potentials evoked by sound stimuli were recorded from the nucleus basalis in the frontal lobe of the pigeon brain. Auditory units in this nucleus showed phasic responses to tonal stimuli and sharp frequency tuning. The latency of responses was 5.8 +/- 0.6 ms. The response properties of these units were similar to those of units in the nucleus mesencephalicus lateralis, pars dorsalis (a mesencephalic auditory nucleus), where fibers from the auditory nuclei in the medulla terminate. This suggests that the nucleus basalis receives projections from medullary auditory neurons. Averaged auditory field potentials in the frontal lobe had three prominent components. Regional changes in the polarity of each component suggest that auditory neurons in the medulla project directly to the nucleus basalis, which in turn projects to the frontal neostriatum.

Anatomical identification of an auditory pathway from a nucleus of the lateral lemniscal system to the frontal telencephalon (nucleus basalis) of the pigeon

Anterograde and retrograde tracing experiments employing WGA-HRP were used to identify an auditory projection area within the frontal telencephalon of the pigeon. The projection originates in a nucleus of the lateral lemniscus, travels with the quintofrontal tract and terminates within nucleus basalis. The location of the projection area and the absence of a thalamic relay in its pathway are consistent with previous reports of short-latency auditory potentials evoked in the vicinity of the nucleus basalis in several avian species.

Telencephalic connections of the trigeminal system in the pigeon (Columba livia): a trigeminal sensorimotor circuit

A combination of autoradiography and horseradish peroxidase histochemistry was used to identify telencephalic structures linking the sensory and motor components of the trigeminal system in the pigeon. A direct telencephalic projection from the principal trigeminal sensory nucleus upon the nucleus basalis via the quintofrontal tract was confirmed. Nucleus basalis projects upon a belt of neurons within the overlying neostriatum. This region (neostriatum frontale, pars trigeminale: NFT) gives rise to the fronto-archistriate tract which terminates both in the archistriatum intermedium and in the overlying neostriatum caudale, medial to the ventricle (neostriatum caudale, pars trigeminale: NCT). NCT projects, in turn, upon a region of archistriatum intermedium containing cell bodies of the occipito-mesencephalic tract. This pathway provides a link between the telencephalon and premotor areas within the lateral (parvicellular) reticular formation of the lower brainstem. The trigeminal sensorimotor circuit defined in these experiments has been implicated by neurobehavioral studies in the control of pecking, grasping, and feeding in the pigeon.

Local auditory evoked potentials and effects of pure tones on click evoked potentials in the pigeon

Local auditory evoked potentials (AEPs) in the pigeon were recorded from the nucleus magnocellularis (NM), nucleus angularis (NA) and Field L with tungsten microelectrodes. In the NM and NA, AEPs in response to clicks were always suppressed by application of continuous pure tones at specific frequencies as is usual for simultaneous masking. In the NA, frequencies of continuous pure tones which produced maximum suppression and frequencies of tone bursts which elicited maximum response both centered around 0.8 kHz. The NM tended to respond similarly. In Field L, however, amplitudes of the AEPs to clicks were suppressed, enhanced, both suppressed and enhanced, or unaffected by presentation of continuous pure tones at specific frequencies. The frequencies of tone bursts which caused maximum AEP were vaguely related to the frequencies of continuous pure tones which elicited maximum suppression of the AEPs to clicks. On the other hand, enhancement was produced by 1-2 kHz continuous pure tones independent of the frequency of tone bursts that produced maximum AEP. It was concluded that enhancement, suppression and lack of effect in Field L were due to some central neural mechanism.

Brain-stem evoked potentials and noise effects in seagulls

Brain-stem auditory evoked potentials (BAEP) recorded from the seagull were large-amplitude, short-latency, vertex-positive deflections which originate in the eighth nerve and several brain-stem nuclei. BAEP waveforms were similar in latency and configurations to that reported for certain other lower vertebrates and some mammals. BAEP recorded at several pure tone frequencies throughout the seagull's auditory spectrum showed an area of heightened auditory sensitivity between 1 and 3 kHz. This range was also found to be the primary bandwidth of the vocalization output of young seagulls. Masking by white noise and pure tones had remarkable effects on several parameters of the BAEP. In general, the tone- and click-induced BAEP were either reduced or obliterated by both pure tone and white noise maskers of specific signal to noise ratios and high intensity levels. The masking effects observed in this study may be related to the manner in which seagulls respond to intense environmental noise. One possible conclusion is that intense environmental noise, such as aircraft engine noise, may severely alter the seagull's localization apparatus and induce sonogenic stress, both of which could cause collisions with low-flying aircraft.

Normal EEG of the restrained twenty-four-hour-old Japanese quail (Coturnix coturnix japonica)

A new method for obtaining bipolar electroencephalographic (EEG) recordings from day-old Japanese quail (Coturnix coturnix japonica) is described. The electrodes are chronically placed stainless steel suture wires sewn into the skull and secured with dental acrylic. Using this arrangement, recordings were made over the hyperstriatum accessorum and dorsoarchistriatum regions of the brain. These records showed a preponderance of high amplitude slow waves. Transitions to low amplitude fast waves were also evident, and rare instances of paradoxical sleep were noted. computerized frequency analyses of the recordings divided wave numbers into distinct groups over the 1 to 17 Hz range: 1 to 4 Hz, 4 to 8 Hz, 8 to 13 Hz, and 13 to 17 Hz. Frequencies of waves detectable across the hyperstriatum accessorum were primarily confined to the 1 to 7 Hz range, whereas waves generated around the dorsoarchistriatus showed more abundant high frequency patterns. Mean amplitude of the waves (10 to 50 muV) showed an inverse exponential relationship with frequency. The method described produced an EEG of good quality on unanesthetized birds with the electrode placement procedures requiring less than 30 min.

Visual evoked potentials from the superficial Wulst of the cockerel to intermittent flash stimulation of various frequencies

Averaged visual evoked potentials (VEPs) from the surface of the Wulst and the electroretinogram (ERG) were recorded simultaneously in curarized cockerels. The polyphasic VEPs were recorded from the dorso-medial region of the Wulst of cockerels at 1 Hz stimulation, while the ERG consisted of the a, b, and c waves. The late VEPs were markedly attenuated with an increase in the stimulation frequency.

Visual receptive field types in the nucleus dorsolateralis anterior of the pigeon's thalamus

Extracellular recordings were made from cells in the dorsolateral thalamus (DLLv, DLLd, DLAmc) of the pigeon, and their receptive field properties analyzed with stationary and moving visual stimuli. One hundred and ten cells were classified as follows on the basis of their responses. I. On-center and off-center cells (56%). Most of the units in this class had a powerful inhibitory surround which decreased the activity generated at the field center and in some cases gave rise to firing when stimulated alone. II. On-off center cells (16%). These gave on-off responses to static stimulation. More than half of them had an inhibitory surround which suppressed both on and off discharge, or in other cases either the on or the off burst of the center response. This group of cells also responded strongly to motion independently of direction. III. Cells sensitive only to motion (28%). The discharges to movements of units in this class were not affected by the direction of motion. The visual properties of the thalamic units are discussed in conjunction with previous results in the optic tectum of the pigeon.

The EEG response to repetitive photic stimulation in various regions of the chicken brain

The EEG response in the chicken to repetitive photic stimulation was studied by frequency analysis and by the averaged response. Evoked responses were observable not only in stations along the visual pathway but also in broad areas apart from the visual pathway. The electrical activity in the archistriatum showed a marked response to flickering stimuli, indicating that this area is involved in the visual function in the chicken. In other telencephalic areas, photically evoked potentials could not be clearly demonstrated in the EEG records. In the hypothalamus and the nucleus rotundus of the diencephalon and in the nucleus reticularis superior of the mesencephalon, sinusoidal waves appeared during stimulation at 8-13/sec. No rhythmic after-discharge was observed following termination of photic stimulation. These finding are indicative of the difference of the visual response in the chicken from previously reported responses in other species.