Susan Greenfield

Scientist • Writer • Broadcaster

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Research Papers

Here are summaries of Susan Greenfield's most prominent scientific research papers. You can download the full list of Susan's published research papers here.

An evaluation of in vivo voltage-sensitive dyes: pharmacological side effects and signal-to-noise ratios after effective removal of brain-pulsation artifacts.

In the current study we investigated pharmacological side effects and signal-to-noise ratios (SNRs) of two commonly used voltage-sensitive dyes, the ‘blue’ dye RH-1691 (1 mg/ml) and the ‘red’ dye di-4-ANEPPS (0.2 mM), applied in vivo to rat barrel cortex. ‘Blue’ dyes are often favored over ‘red’ dyes in in vivo studies due to their apparent superior SNR, partly because their fluorescence spectrum is farther away from the hemoglobin absorption spectrum, making them less prone to heartbeat-associated brain pulsation artifacts (BPA). We implemented a previously reported template-based BPA removal algorithm, and evaluated its applicability to di-4-ANEPPS, before comparing characteristics of the two dyes. Somatosensory-evoked potentials (SEPs) were also recorded. Whilst SEPs recorded before and after application of di-4-ANEPPS failed to exhibit demonstrable differences, RH-1691 caused a significant and prolonged increase in SEP amplitude for several hours. In contrast, neither dye influenced the spontaneous cortical activity as assessed by the spectral content of the EEG. Both dyes turned out to be strikingly similar with respect to changes in fractional fluorescence as a function of SEP response amplitude, as well as regarding shot noise characteristics after removal of the BPA. Thus there is strong evidence that the increased SNR for RH-1691 is a consequence of artificially increased signal. When applying an appropriate BPA removal algorithm, di-4-ANEPPS has proven to be suitable for single trial in vivo VSDI and produces no detectable neurophysiological changes in the system under investigation. Taken together, our data argue for a careful re-evaluation of pharmacological side effects of RH-1691 and support the applicability of di-4-ANEPPS for stable single trial in vivo VSDI recordings.

Ref: Grandy, T.H., Greenfield, S.A., and Devonshire, I.M.

 

A neuroscientific approach to consciousness.

For a neuroscientist, consciousness currently defies any formal operational definition. However, the phenomenon is distinct from self-consciousness: after all, one can "let oneself go," when experiencing extreme emotion, but still be accessing a sentiment, subjective, conscious state. This raw, basic subjective state does not appear to be an exclusive property of the human brain. There is no obvious qualitative transformation in either the anatomy or the physiology of the central nervous system of human or non-human animals, no phylogenetic Rubicon in the animal kingdom. Similarly, there is no clear ontogenetic line that is crossed as the brain grows in the womb, no single event or change in brain physiology, and certainly not at birth, when consciousness might be generated in an all-or-none fashion. A more plausible, and scientific, view of consciousness might be therefore that it is not a different property of the brain, some magic bullet, but that it is a consequence of a quantitative increase in the complexity of the human brain: consciousness will grow as brains grow. Hence, consciousness is most likely to be a continuously variable property of the brain, in both phylogenetic and ontogenetic terms. Here, we describe how modern techniques may be utilized to determine the physiological basis of consciousness.

Ref: Greenfield, S. A. & Collins, T. F. A neuroscientific approach to consciousness. Prog Brain Res 150, 11-23, doi:10.1016/S0079-6123(05)50002-5 (2005).

 

From Scientific Theory to Classroom Practice.

The importance of neuroscience in education is becoming widely recognized by both neuroscientists and educators. However, to date, there has been little effective collaboration between the two groups, resulting in the spread of ideas in education poorly based on neuroscience. For their part, educators are often too busy to develop sufficient scientific literacy, and neuroscientists are put off collaborations with risk of overinterpretation of their work. We designed and led a successful 6-month collaborative project between educators and neuroscientists. The project consisted of a series of seminars on topics chosen by both parties such as the neuroscience of attention, learning, and memory and aimed to create a dialog between the two. Here, we report that all teachers found the seminars relevant to their practice and that the majority felt the information was presented in an accessible manner. Such was the success of the project that teachers felt there were direct changes in their classroom practice as a consequence and that the course should be more widely available. We suggest that this format of co-constructed dialog allows for lucrative collaborations between neuroscientists and educators and may be a step to bridging the waters that separate these intrinsically linked disciplines.

Ref: Dommett, E. J., Devonshire, I. M., Plateau, C. R., Westwell, M. S. & Greenfield, S. A. From Scientific Theory to Classroom Practice. The Neuroscientist 17, 382-388, doi:10.1177/1073858409356111 (2011).

 

Environmental enrichment differentially modifies specific components of sensory-evoked activity in rat barrel cortex as revealed by simultaneous electrophysiological recordings and optical imaging in vivo.

Environmental enrichment of laboratory animals leads to multi-faceted changes to physiology, health and disease prognosis. An important and under-appreciated factor in enhancing cognition through environmental manipulation may be improved basic sensory function. Previous studies have highlighted changes in cortical sensory map plasticity but have used techniques such as electrophysiology, which suffer from poor spatial resolution, or optical imaging of intrinsic signals, which suffers from low temporal resolution. The current study attempts to overcome these limitations by combining voltage-sensitive dye imaging with somatosensory-evoked potential (SEP) recordings: the specific aim was to investigate sensory function in barrel cortex using multi-frequency whisker stimulation under urethane anaesthesia. Three groups of rats were used that each experienced a different level of behavioural or environmental enrichment. We found that enrichment increased all SEP response components subsequent to the initial thalamocortical input, but only when evoked by single stimuli; the thalamocortical component remained unchanged across all animal groups. The optical signal exhibited no changes in amplitude or latency between groups, resembling the thalamocortical component of the SEP response. Permanent and extensive changes to housing conditions conferred no further enhancement to sensory function above that produced by the milder enrichment of regular handling and behavioural testing, a finding with implications for improvements in animal welfare through practical changes to animal husbandry.

Ref: Devonshire, I. M., Dommett, E. J., Grandy, T. H., Halliday, A. C. & Greenfield, S. A. Environmental enrichment differentially modifies specific components of sensory-evoked activity in rat barrel cortex as revealed by simultaneous electrophysiological recordings and optical imaging in vivo.Neuroscience 170, 662-669, doi:10.1016/j.neuroscience.2010.07.029 (2010)

 

An acetylcholinesterase-derived peptide inhibits endocytic membrane activity in a human metastatic breast cancer cell line.

Acetylcholinesterase (AChE) is well established as having non-cholinergic functions and is also expressed in breast tumours where its function(s) is not known. Recently, a candidate peptide sequence towards the C-terminal of the AChE molecule has been identified, as the salient site remote from normal catalysis in neurons, and possibly other cells. The main aim of this study was to explore the possibility that 'AChE-peptide' might also affect human breast cancer cells. Uptake of the non-cytotoxic tracer horseradish peroxidase (HRP) was used as an index of endocytosis, a key component of the metastatic cascade, representing exocytosis/secretory membrane activity and/or plasma membrane protein turnover. AChE-peptide had no affect on the weakly metastatic MCF-7 human breast cancer cell line. By contrast, application of AChE-peptide to the strongly metastatic MDA-MB-231 cells resulted in a dose-dependent inhibition of HRP uptake; treatment with a scrambled variant of the peptide of comparable amino acid length was ineffective. The action of AChE-peptide was suppressed by lowering the extracellular Ca2+ concentration and co-applying a selective antagonist of alpha7, but not alpha4/beta2, nicotinic receptor. The results suggest that AChE-peptide has a novel, selective bioactivity on breast cancer cells and can potentiate metastatic cell behaviour.

Ref: Onganer, P. U., Djamgoz, M. B., Whyte, K. & Greenfield, S. A. An acetylcholinesterase-derived peptide inhibits endocytic membrane activity in a human metastatic breast cancer cell line. Biochim Biophys Acta 1760, 415-420, doi:10.1016/j.bbagen.2005.12.016 (2006).

 

Parkinson's disease, Alzheimer's disease and motor neurone disease: identifying a common mechanism.

Although Alzheimer's disease, Parkinson's disease, and motor neurone disease are distinct disorders, there could be a common neurodegenerative mechanism that characterises the death of selective neurone populations in each case. We propose that this mechanism could be an aberrantly activated, developmental process involving a non-classical, non-enzymatic action of acetylcholinesterase mediated via a short linear motif near the C-terminal end of the molecule. Since this motif has a highly conserved homology with part of the amyloid precursor protein, it may be particularly attractive as a target for novel therapeutic strategies in neurodegeneration.

Ref: Greenfield, S. & Vaux, D. J. Parkinson's disease, Alzheimer's disease and motor neurone disease: identifying a common mechanism. Neuroscience113, 485-492 (2002).

 

Dopamine release and uptake dynamics within nonhuman primate striatum in vitro.

The putamen of the human striatum is a heterogeneous nucleus that contains the primary site of loss of dopamine (DA) in Parkinson's disease (PD). Furthermore, different functional domains of the putamen are heterogeneously susceptible to DA loss, and yet the dynamic regulation of extracellular DA concentration ([DA](o)) and comparison between domains has not been explored in the primate brain. In these studies, DA was measured in real time using fast-scan cyclic voltammetry at a carbon-fiber microelectrode in vitro in striatal sections from the common marmoset (Callithrix jacchus). [DA](o) released by a single stimulus pulse varied threefold along a ventromedial-dorsolateral axis. DA uptake was via the DA transporter (GBR12909 sensitive, desipramine insensitive). On the basis of data modeling with simulations of Michaelis-Menten kinetics, rate maximum, V(max), varied with region: both [DA](o) and V(max) were greatest in regions most vulnerable in PD. These differences were reflected in part by regional variation in DA content. [DA](o), V(max), and regional variation were two- to threefold greater than in rodent caudatoputamen. In addition, steady-state [DA](o) at physiological firing rates in primate striatum was controlled by depolarization frequency, uptake, and presynaptic autoreceptors. Furthermore, regulation of [DA](o) by these mechanisms differed significantly between limbic- and motor-associated domains. These data indicate interspecies heterogeneity in striatal DA dynamics that must be considered when extrapolating behavioral and drug responses from rodent to the primate brain. Moreover, the heterogeneity demonstrated within the primate putamen in the availability and dynamic regulation of DA may be central to understanding DA function in health, cocaine abuse, and disease.

Ref: Cragg, S. J., Hille, C. J. & Greenfield, S. A. Dopamine release and uptake dynamics within nonhuman primate striatum in vitro. J Neurosci 20, 8209-8217 (2000).